Harrison's Cardiovascular Medicine

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HARRISON’S Cardiovascular Medicine

Derived from Harrison’s Principles of Internal Medicine, 17th Edition

Editors ANTHONY S. FAUCI, MD Chief, Laboratory of Immunoregulation; Director, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda

DENNIS L. KASPER, MD William Ellery Channing Professor of Medicine, Professor of Microbiology and Molecular Genetics, Harvard Medical School; Director, Channing Laboratory, Department of Medicine, Brigham and Women’s Hospital, Boston

DAN L. LONGO, MD Scientific Director, National Institute on Aging, National Institutes of Health, Bethesda and Baltimore

EUGENE BRAUNWALD, MD Distinguished Hersey Professor of Medicine, Harvard Medical School; Chairman,TIMI Study Group, Brigham and Women’s Hospital, Boston

STEPHEN L. HAUSER, MD Robert A. Fishman Distinguished Professor and Chairman, Department of Neurology, University of California, San Francisco

J. LARRY JAMESON, MD, PhD Professor of Medicine; Vice President for Medical Affairs and Lewis Landsberg Dean, Northwestern University Feinberg School of Medicine, Chicago

JOSEPH LOSCALZO, MD, PhD Hersey Professor of Theory and Practice of Medicine, Harvard Medical School; Chairman, Department of Medicine; Physician-in-Chief, Brigham and Women’s Hospital, Boston

HARRISON’S Cardiovascular Medicine Editor

Joseph Loscalzo, MD, PhD Hersey Professor of Theory and Practice of Medicine, Harvard Medical School; Chairman, Department of Medicine; Physician-in-Chief, Brigham and Women’s Hospital, Boston

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CONTENTS Contributors. . . . . . . . . . . . . . . . . . . . . . . . vii

13 Diagnostic Cardiac Catheterization and Angiography . . . . . . . . . . . . . . . . . . . . . . . . . . 112 Donald S. Baim

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix SECTION I

SECTION III

INTRODUCTION TO CARDIOVASCULAR DISORDERS

HEART RHYTHM DISTURBANCES 14 Principles of Electrophysiology . . . . . . . . . . . . 122 Gordon F.Tomaselli

1 Basic Biology of the Cardiovascular System . . . . . 2 Joseph Loscalzo, Peter Libby, Eugene Braunwald

15 The Bradyarrhythmias . . . . . . . . . . . . . . . . . . . 132 Gordon F.Tomaselli

2 Epidemiology of Cardiovascular Disease . . . . . . . 18 Thomas A. Gaziano, J. Michael Gaziano

16 The Tachyarrhythmias . . . . . . . . . . . . . . . . . . . 147 Francis Marchlinski

3 Approach to the Patient with Possible Cardiovascular Disease. . . . . . . . . . . . . . . . . . . . 26 Eugene Braunwald

SECTION IV

SECTION II

DISORDERS OF THE HEART

DIAGNOSIS OF CARDIOVASCULAR DISORDERS

17 Heart Failure and Cor Pulmonale. . . . . . . . . . . 178 Douglas L. Mann

4 Chest Discomfort . . . . . . . . . . . . . . . . . . . . . . . 32 Thomas H. Lee

18 Cardiac Transplantation and Prolonged Assisted Circulation . . . . . . . . . . . . . . . . . . . . . 198 Sharon A. Hunt

5 Dyspnea and Pulmonary Edema. . . . . . . . . . . . . 40 Richard M. Schwartzstein

19 Congenital Heart Disease in the Adult . . . . . . . 203 John S. Child

6 Hypoxia and Cyanosis . . . . . . . . . . . . . . . . . . . . 47 Eugene Braunwald

20 Valvular Heart Disease . . . . . . . . . . . . . . . . . . . 215 Patrick O’Gara, Eugene Braunwald

7 Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Eugene Braunwald, Joseph Loscalzo

21 Cardiomyopathy and Myocarditis . . . . . . . . . . . 241 Joshua Wynne, Eugene Braunwald

8 Palpitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 Joseph Loscalzo

22 Pericardial Disease . . . . . . . . . . . . . . . . . . . . . . 254 Eugene Braunwald

9 Physical Examination of the Cardiovascular System . . . . . . . . . . . . . . . . . . . . 62 Robert A. O’Rourke, Eugene Braunwald

23 Tumors and Trauma of the Heart . . . . . . . . . . . 265 Eric H.Awtry,Wilson S. Colucci

10 Approach to the Patient with a Heart Murmur . . . . . . . . . . . . . . . . . . . . . . . . . 72 Patrick T. O’Gara, Eugene Braunwald

24 Cardiac Manifestations of Systemic Disease . . . . 270 Eric H.Awtry,Wilson S. Colucci 25 Infective Endocarditis . . . . . . . . . . . . . . . . . . . 275 Adolf W. Karchmer

11 Electrocardiography. . . . . . . . . . . . . . . . . . . . . . 86 Ary L. Goldberger

26 Acute Rheumatic Fever. . . . . . . . . . . . . . . . . . 290 Jonathan R. Carapetis

12 Noninvasive Cardiac Imaging: Echocardiography, Nuclear Cardiology, and MRI/CT Imaging . . . . 99 Rick A. Nishimura, Raymond J. Gibbons, James F. Glockner,A. Jamil Tajik

27 Chagas’ Disease . . . . . . . . . . . . . . . . . . . . . . . . 297 Louis V. Kirchhoff

v

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Contents

28 Cardiogenic Shock and Pulmonary Edema . . . . 302 Judith S. Hochman, David H. Ingbar

38 Diseases of the Aorta . . . . . . . . . . . . . . . . . . . . 445 Mark A. Creager, Joseph Loscalzo

29 Cardiovascular Collapse, Cardiac Arrest, and Sudden Cardiac Death. . . . . . . . . . . . . . . . 311 Robert J. Myerburg,Agustin Castellanos

39 Vascular Diseases of the Extremities . . . . . . . . . 454 Mark A. Creager, Joseph Loscalzo

SECTION V

DISORDERS OF THE VASCULATURE 30 The Pathogenesis, Prevention, and Treatment of Atherosclerosis. . . . . . . . . . . . . . . 322 Peter Libby 31 Disorders of Lipoprotein Metabolism . . . . . . . . 335 Daniel J. Rader, Helen H. Hobbs 32 The Metabolic Syndrome . . . . . . . . . . . . . . . . 358 Robert H. Eckel 33 Ischemic Heart Disease . . . . . . . . . . . . . . . . . . 366 Elliott M.Antman,Andrew P. Selwyn, Eugene Braunwald, Joseph Loscalzo 34 Unstable Angina and Non-ST-Elevation Myocardial Infarction . . . . . . . . . . . . . . . . . . . 387 Christopher P. Cannon, Eugene Braunwald 35 ST-Segment Elevation Myocardial Infarction . . . 395 Elliott M.Antman, Eugene Braunwald 36 Percutaneous Coronary Intervention . . . . . . . . 414 Donald S. Baim 37 Hypertensive Vascular Disease. . . . . . . . . . . . . . 422 Theodore A. Kotchen

40 Pulmonary Hypertension. . . . . . . . . . . . . . . . . 467 Stuart Rich SECTION VI

CARDIOVASCULAR ATLASES 41 Atlas of Electrocardiography. . . . . . . . . . . . . . . 478 Ary L. Goldberger 42 Atlas of Noninvasive Cardiac Imaging . . . . . . . 495 Rick A. Nishimura, Raymond J. Gibbons, James F. Glockner,A. Jamil Tajik 43 Atlas of Cardiac Arrhythmias . . . . . . . . . . . . . . 504 Ary L. Goldberger 44 Atlas of Percutaneous Revascularization . . . . . . 517 Donald S. Baim Appendix Laboratory Values of Clinical Importance . . . . . 523 Alexander Kratz, Michael A. Pesce, Daniel J. Fink Review and Self-Assessment . . . . . . . . . . . . . . . 545 Charles Wiener, Gerald Bloomfield, Cynthia D. Brown, Joshua Schiffer,Adam Spivak Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 593

CONTRIBUTORS Numbers in brackets refer to the chapter(s) written or co-written by the contributor. DANIEL J. FINK,† MD, MPH Associate Professor of Clinical Pathology, College of Physicians and Surgeons, Columbia University, New York [Appendix]

ELLIOTT M. ANTMAN, MD Professor of Medicine, Harvard Medical School; Director, Samuel L. Levine Cardiac Unit, and Senior Investigator,TIMI Study Group, Brigham and Women’s Hospital, Boston [33, 35]

J. MICHAEL GAZIANO, MD, MPH Chief, Division of Aging, Brigham and Women’s Hospital; Director, Massachusetts Veterans Epidemiology, Research and Information Center (MAVERIC) and Geriatric Research, Education and Clinical Center (GRECC), Boston VA Healthcare System;Associate Professor of Medicine, Harvard Medical School, Boston [2]

ERIC H. AWTRY, MD Assistant Professor of Medicine, Boston University School of Medicine, Boston [23, 24] DONALD S. BAIM, MD † Professor of Medicine, Harvard Medical School; Executive Vice President, Chief Medical and Scientific Officer, Boston Scientific Corporation, Natick [13, 36, 44]

THOMAS A. GAZIANO, MD, MSc Instructor in Medicine, Harvard Medical School;Associate Physician of Cardiovascular Medicine, Brigham and Women’s Hospital, Boston [2]

GERALD BLOOMFIELD, MD, MPH Department of Internal Medicine,The Johns Hopkins University School of Medicine, Baltimore [Review and Self-Assessment]

RAYMOND J. GIBBONS, MD Arthur M. and Gladys D. Gray Professor of Medicine, Mayo Clinic College of Medicine; Consultant, Cardiovascular Diseases, Mayo Clinic, Rochester [12, 42]

EUGENE BRAUNWALD, MD, MA (Hon), ScD (Hon) Distinguished Hersey Professor of Medicine, Harvard Medical School; Chairman,TIMI Study Group, Brigham and Women’s Hospital, Boston [1, 3, 6, 7, 9, 10, 20, 21, 22, 33, 34, 35]

JAMES F. GLOCKNER, MD Assistant Professor of Radiology, Mayo Clinic College of Medicine, Rochester [12, 42]

CYNTHIA D. BROWN, MD Department of Internal Medicine,The Johns Hopkins University School of Medicine, Baltimore [Review and Self-Assessment]

ARY L. GOLDBERGER, MD Professor of Medicine, Harvard Medical School;Associate Director, Division of Interdisciplinary Medicine and Biotechnology, Beth Israel Deaconess Medical Center, Boston [11, 41, 43]

CHRISTOPHER P. CANNON, MD Associate Professor of Medicine, Harvard Medical School;Associate Physician, Cardiovascular Division, Senior Investigator,TIMI Study Group, Brigham and Women’s Hospital, Boston [34]

HELEN H. HOBBS, MD Investigator, Howard Hughes Medical Institute; Professor of Internal Medicine and Molecular Genetics, University of Texas Southwestern Medical Center, Dallas [31]

JONATHAN R. CARAPETIS, MBBS, PhD Director, Menzies School of Health Research; Professor, Charles Darwin University,Australia [26] AGUSTIN CASTELLANOS, MD Professor of Medicine; Director, Clinical Electrophysiology, University of Miami Miller School of Medicine, Miami [29]

JUDITH S. HOCHMAN, MD Harold Synder Family Professor of Cardiology; Clinical Chief, the Leon H. Charney Division of Cardiology; New York University School of Medicine; Director, Cardiovascular Clinical Research, New York [28]

JOHN S. CHILD, MD Director,Ahmanson-UCLA Adult Congenital Heart Disease Center; Streisand Professor of Medicine and Cardiology, David Geffen School of Medicine at UCLA, Los Angeles [19]

SHARON A. HUNT, MD Professor, Cardiovascular Medicine, Stanford University, Palo Alto [18]

WILSON S. COLUCCI, MD Thomas J. Ryan Professor of Medicine, Boston University School of Medicine; Chief, Cardiovascular Medicine, Boston University Medical Center, Boston [23, 24]

DAVID H. INGBAR, MD Professor of Medicine, Physiology & Pediatrics; Director, Pulmonary, Allergy, Critical Care & Sleep Division; Executive Director, Center for Lung Science & Health, University of Minnesota School of Medicine; Co-Director, Medical ICU & Respiratory Care, University of Minnesota Medical Center, Fairview [28]

MARK A. CREAGER, MD Professor of Medicine, Harvard Medical School; Simon C. Fireman Scholar in Cardiovascular Medicine; Director,Vascular Center, Brigham and Women’s Hospital, Boston [38, 39] ROBERT H. ECKEL, MD Professor of Medicine, Division of Endocrinology, Metabolism and Diabetes, Division of Cardiology; Professor of Physiology and Biophysics; Charles A. Boettcher II Chair in Atherosclerosis; Program Director,Adult General Clinical Research Center, University of Colorado at Denver and Health Sciences Center; Director Lipid Clinic, University Hospital,Aurora [32] †

ADOLF W. KARCHMER, MD Professor of Medicine, Harvard Medical School, Boston [25] LOUIS V. KIRCHHOFF, MD, MPH Professor, Departments of Internal Mediciene and Epidemiology, University of Iowa; Staff Physician, Department of Veterans Affairs Medical Center, Iowa City [27]

Deceased

vii

viii

Contributors

THEODORE A. KOTCHEN, MD Associate Dean for Clinical Research; Director, General Clinical Research Center, Medical College of Wisconsin,Wisconsin [37] ALEXANDER KRATZ, MD, PhD, MPH Assistant Professor of Clinical Pathology, Columbia University College of Physicians and Surgeons;Associate Director, Core Laboratory, Columbia University Medical Center, New York-Presbyterian Hospital; Director,Allen Pavilion Laboratory, New York [Appendix] THOMAS H. LEE, MD Professor of Medicine, Harvard Medical School; Chief Executive Officer, Partners Community Health Care, Inc; Network President, Partners Health Care, Boston [4] PETER LIBBY, MD Mallinckrodt Professor of Medicine, Harvard Medical School; Chief, Cardiovascular Medicine, Brigham and Women’s Hospital, Boston [1, 30] JOSEPH LOSCALZO, MD, PhD, MA (Hon) Hersey Professor of the Theory and Practice of Medicine, Harvard Medical School; Chairman, Department of Medicine, Physician-inChief, Brigham and Women’s Hospital, Boston [1, 7, 8, 33, 38, 39]

MICHAEL A. PESCE, PhD Clinical Professor of Pathology, Columbia University College of Physicians and Surgeons; Director of Specialty Laboratory, New York Presbyterian Hospital, Columbia University Medical Center, New York [Appendix] DANIEL J. RADER, MD Cooper-McClure Professor of Medicine, University of Pennsylvania School of Medicine, Philadelphia [31] STUART RICH, MD Professor of Medicine, Section of Cardiology, University of Chicago, Chicago [40] JOSHUA SCHIFFER, MD Department of Internal Medicine,The Johns Hopkins University School of Medicine, Baltimore [Review and Self-Assessment] RICHARD M. SCHWARTZSTEIN, MD Professor of Medicine, Harvard Medical School;Associate Chair, Pulmonary and Critical Care Medicine;Vice-President for Education, Beth Israel Deaconess Medical Center, Boston [5] ANDREW P. SELWYN, MA, MD Professor of Medicine, Harvard Medical School, Boston [33]

DOUGLAS L. MANN, MD Professor of Medicine, Molecular Physiology and Biophysics; Chief, Section of Cardiology, Baylor College of Medicine, St. Luke’s Episcopal Hospital and Texas Heart Institute, Houston [17]

ADAM SPIVAK, MD Department of Internal Medicine,The Johns Hopkins University School of Medicine, Baltimore [Review and Self-Assessment]

FRANCIS MARCHLINSKI, MD Professor of Medicine; Director of Cardiac Electrophysiology, University of Pennsylvania Health System, University of Pennsylvania School of Medicine, Philadelphia [16]

A. JAMIL TAJIK, MD Thomas J.Watson, Jr., Professor; Professor of Medicine and Pediatrics; Chairman (Emeritus), Zayed Cardiovascular Center, Mayo Clinic, Rochester, Minnesota; Consultant, Cardiovascular Division, Mayo Clinic, Scottsdale [12, 42]

ROBERT J. MYERBERG, MD Professor of Medicine and Physiology;AHA Chair in Cardiovascular Research, University of Miami Miller School of Medicine, Miami [29] RICK A. NISHIMURA, MD Judd and Mary Morris Leighton Professor of Cardiovascular Diseases; Professor of Medicine, Mayo Clinic College of Medicine, Rochester [12, 42] PATRICK T. O’GARA, MD Associate Professor of Medicine, Harvard Medical School; Director, Clinical Cardiology, Brigham and Women’s Hospital, Boston [10, 20] ROBERT A. O’ROURKE, MD Distinguished Professor of Medicine Emeritus, University of Texas Health Science Center, San Antonio [9]

GORDON F. TOMASELLI, MD David J. Carver Professor of Medicine,Vice Chairman, Department of Medicine for Research,The Johns Hopkins University, Baltimore [14, 15] CHARLES WIENER, MD Professor of Medicine and Physiology;Vice Chair, Department of Medicine; Director, Osler Medical Training Program,The Johns Hopkins University School of Medicine, Baltimore [Review and Self-Assessment] JOSHUA WYNNE, MD, MBA, MPH Executive Associate Dean, Professor of Medicine, University of North Dakota School of Medicine and Health Sciences, Grand Forks [21]

PREFACE Cardiovascular disease is the leading cause of death in the United States, and is rapidly becoming a major cause of death in the developing world. Advances in the therapy and prevention of cardiovascular diseases have clearly improved the lives of patients with these common, potentially devastating disorders; yet, the disease prevalence and the risk factor burden for disease (especially obesity in the United States and smoking worldwide) continue to increase globally. Cardiovascular medicine is, therefore, of crucial importance to the field of internal medicine. Cardiovascular medicine is a large and growing subspecialty, and comprises a number of specific subfields, including coronary heart disease, congenital heart disease, valvular heart disease, cardiovascular imaging, electrophysiology, and interventional cardiology. Many of these areas involve novel technologies that facilitate diagnosis and therapy. The highly specialized nature of these disciplines within cardiology and the increasing specialization of cardiologists argue for the importance of a broad view of cardiovascular medicine by the internist in helping to guide the patient through illness and the decisions that arise in the course of its treatment. The scientific underpinnings of cardiovascular medicine have also been evolving rapidly. The molecular pathogenesis and genetic basis for many diseases are now known and, with this knowledge, diagnostics and therapeutics are becoming increasingly individualized. Cardiovascular diseases are largely complex phenotypes, and this structural and physiological complexity recapitulates the complex molecular and genetic systems that underlie it. As knowledge about these complex systems

expands, the opportunity for identifying unique therapeutic targets increases, holding great promise for definitive interventions in the future. Regenerative medicine is another area of cardiovascular medicine that is rapidly achieving translation. Recognition that the adult human heart can repair itself, albeit sparingly with typical injury, and that cardiac precursor (stem) cells reside within the myocardium to do this can be expanded, and can be used to repair if not regenerate a normal heart is an exciting advance in the field. These concepts represent a completely novel paradigm that will revolutionize the future of the subspecialty. In view of the importance of cardiovascular medicine to the field of internal medicine, and the rapidity with which the scientific basis for the discipline is advancing, Harrison’s Cardiovascular Medicine was developed. The purpose of this sectional is to provide the readers with a succinct overview of the field of cardiovascular medicine. To achieve this goal, Harrison’s Cardiovascular Medicine comprises the key cardiovascular chapters contained in Harrison’s Principles of Internal Medicine, 17e, contributed by leading experts in the field.This sectional is designed not only for physicians-in-training on cardiology rotations, but also for practicing clinicians, other health care professionals, and medical students who seek to enrich and update their knowledge of this rapidly changing field. The editors trust that this book will increase both the readers’ knowledge of the field, and their appreciation for its importance. Joseph Loscalzo, MD, PhD

ix

NOTICE Medicine is an ever-changing science. As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy are required. The authors and the publisher of this work have checked with sources believed to be reliable in their efforts to provide information that is complete and generally in accord with the standards accepted at the time of publication. However, in view of the possibility of human error or changes in medical sciences, neither the authors nor the publisher nor any other party who has been involved in the preparation or publication of this work warrants that the information contained herein is in every respect accurate or complete, and they disclaim all responsibility for any errors or omissions or for the results obtained from use of the information contained in this work. Readers are encouraged to confirm the information contained herein with other sources. For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this work is accurate and that changes have not been made in the recommended dose or in the contraindications for administration. This recommendation is of particular importance in connection with new or infrequently used drugs.

Review and self-assessment questions and answers were taken from Wiener C, Fauci AS, Braunwald E, Kasper DL, Hauser SL, Longo DL, Jameson JL, Loscalzo J (editors) Bloomfield G, Brown CD, Schiffer J, Spivak A (contributing editors). Harrison’s Principles of Internal Medicine Self-Assessment and Board Review, 17th ed. New York, McGraw-Hill, 2008, ISBN 978-0-07-149619-3.

The global icons call greater attention to key epidemiologic and clinical differences in the practice of medicine throughout the world. The genetic icons identify a clinical issue with an explicit genetic relationship.

SECTION I

INTRODUCTION TO CARDIOVASCULAR DISORDERS

CHAPTER 1

BASIC BIOLOGY OF THE CARDIOVASCULAR SYSTEM Joseph Loscalzo

■

Peter Libby

■ The Blood Vessel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Vascular Ultrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Origin of Vascular Cells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Vascular Cell Biology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Vascular Smooth-Muscle Cell . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Vascular Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Vascular Pharmacogenomics . . . . . . . . . . . . . . . . . . . . . . . . . . 8 ■ Cellular Basis of Cardiac Contraction . . . . . . . . . . . . . . . . . . . . 8 The Cardiac Ultrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

■

Eugene Braunwald

The Contractile Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Cardiac Activation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 ■ Control of Cardiac Performance and Output . . . . . . . . . . . . . . 13 ■ Assessment of Cardiac Function . . . . . . . . . . . . . . . . . . . . . . . 15 Diastolic Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Cardiac Metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Regenerating Cardiac Tissue . . . . . . . . . . . . . . . . . . . . . . . . . 17 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

The tone of muscular arterioles regulates blood pressure and flow through various arterial beds.These smaller arteries have relatively thick tunica media in relation to the adventitia (Fig. 1-1C). Medium-size muscular arteries likewise contain a prominent tunica media (Fig. 1-1D). Atherosclerosis commonly affects this type of muscular artery.The larger elastic arteries have a much more structured tunica media consisting of concentric bands of smoothmuscle cells interspersed with strata of elastin-rich extracellular matrix sandwiched between continuous layers of smooth-muscle cells (Fig. 1-1E). Larger arteries have a clearly demarcated internal elastic lamina that forms the barrier between the intima and media.An external elastic lamina demarcates the media of arteries from the surrounding adventitia.

THE BLOOD VESSEL VASCULAR ULTRASTRUCTURE Blood vessels participate in homeostasis on a moment-tomoment basis and contribute to the pathophysiology of diseases of virtually every organ system. Hence, an understanding of the fundamentals of vascular biology furnishes a foundation for understanding normal function of all organ systems and many diseases. The smallest blood vessels, capillaries, consist of a monolayer of endothelial cells in close juxtaposition with occasional smoothmuscle–like cells known as pericytes (Fig. 1-1A). Unlike larger vessels, pericytes do not invest the entire microvessel to form a continuous sheath.Veins and arteries typically have a trilaminar structure (Fig. 1-1B–E). The intima consists of a monolayer of endothelial cells continuous with those of the capillary trees. The middle layer, or tunica media, consists of layers of smooth-muscle cells; in veins, this layer can contain just a few layers of smoothmuscle cells (Fig. 1-1B). The outer layer, the adventitia, consists of looser extracellular matrix with occasional fibroblasts, mast cells, and nerve terminals. Larger arteries have their own vasculature, the vasa vasorum, which nourish the outer aspects of the tunica media. The adventitia of many veins surpasses the intima in thickness.

ORIGIN OF VASCULAR CELLS The intima in human arteries often contains occasional resident smooth-muscle cells beneath the monolayer of vascular endothelial cells. The embryonic origin of smooth-muscle cells in various types of artery differs. Some upper-body arterial smooth-muscle cells derive from the neural crest, whereas lower-body arteries generally recruit smooth-muscle cells during development from neighboring mesodermal structures, such as the

2

3

Pericyte

Endothelial cell

A. Capillary

B. Vein

C. Small muscular artery

External elastic lamina

Adventitia

D. Large muscular artery

somites. Recent evidence suggests that the bone marrow may give rise to both vascular endothelial cells and smooth-muscle cells, particularly under conditions of repair of injury or vascular lesion formation. Indeed, the ability of bone marrow to repair an injured endothelial monolayer may contribute to maintenance of vascular health and may promote arterial disease when this reparative mechanism fails due to injurious stimuli or age.The precise sources of endothelial and mesenchymal progenitor cells or their stem cell precursors remain the subject of active investigation.

VASCULAR CELL BIOLOGY Endothelial Cell The key cell of the vascular intima, the endothelial cell, has manifold functions in health and disease. Most obviously, the endothelium forms the interface between tissues and the blood compartment. It must, therefore, regulate the entry of molecules and cells into tissues in a selective manner.The ability of endothelial cells to serve as a permselective barrier fails in many vascular disorders, including atherosclerosis and hypertension. This dysregulation of permselectivity also occurs in pulmonary edema and other situations of “capillary leak.”

E. Large elastic artery

D. Larger muscular arteries have a prominent media with smooth-muscle cells embedded in a complex extracellular matrix. E. Larger elastic arteries have circular layers of elastic tissue alternating with concentric rings of smooth-muscle cells.

The endothelium also participates in the local regulation of blood flow and vascular caliber. Endogenous substances produced by endothelial cells, such as prostacyclin, endothelium-derived hyperpolarizing factor, and nitric oxide (NO), provide tonic vasodilatory stimuli under physiologic conditions in vivo (Table 1-1). Impaired production or excess catabolism of NO impairs this endothelium-dependent vasodilator function and may contribute to excessive vasoconstriction under various pathologic situations. By contrast, endothelial cells also produce potent vasoconstrictor substances such as endothelin in a regulated fashion. Excessive production of reactive oxygen species, such as superoxide anion (O2–), by endothelial or smooth-muscle cells under pathologic conditions (e.g., excessive exposure to angiotensin II) can promote local oxidative stress and inactivate NO. The endothelial monolayer contributes critically to inflammatory processes involved in normal host defenses and pathologic states. The normal endothelium resists prolonged contact with blood leukocytes; however, when activated by bacterial products, such as endotoxin or proinflammatory cytokines released during infection or injury, endothelial cells express an array of leukocyte adhesion molecules that bind various classes of leukocytes. The endothelial cells appear to recruit selectively

Basic Biology of the Cardiovascular System

Internal elastic lamina

FIGURE 1-1 Schematics of the structures of various types of blood vessels. A. Capillaries consist of an endothelial tube in contact with a discontinuous population of pericytes. B. Veins typically have thin medias and thicker adventitias. C. A small muscular artery consists of a prominent tunica media.

CHAPTER 1

Vascular smoothmuscle cell

4

TABLE 1-1 ENDOTHELIAL FUNCTIONS IN HEALTH AND DISEASE

SECTION I Introduction to Cardiovascular Disorders

HOMEOSTATIC PHENOTYPE

DYSFUNCTIONAL PHENOTYPE

Vasodilatation Antithrombotic, profibrinolytic Anti-inflammatory Antiproliferative Antioxidant

Impaired dilatation, vasoconstriction Prothrombotic, antifibrinolytic Proinflammatory Proproliferative Prooxidant

different classes of leukocytes under different pathologic conditions.The gamut of adhesion molecules and chemokines generated during acute bacterial processes tends to recruit granulocytes. In chronic inflammatory diseases, such as tuberculosis or atherosclerosis, endothelial cells express adhesion molecules that favor the recruitment of mononuclear leukocytes that characteristically accumulate in these conditions. The endothelial monolayer also dynamically regulates thrombosis and hemostasis. NO, in addition to its vasodilatory properties, can limit platelet activation and aggregation. Like NO, prostacyclin produced by endothelial cells under normal conditions not only provides a vasodilatory stimulus but also antagonizes platelet activation and aggregation.Thrombomodulin expressed on the surface of endothelial cells binds thrombin at low concentrations and inhibits coagulation through activation of the protein C pathway, leading to enhanced catabolism of clotting factors Va and VIIIa, thereby combating thrombus formation.The surface of endothelial cells contains heparan sulfate glycosaminoglycans that furnish an endogenous antithrombin coating to the vasculature. Endothelial cells also participate actively in fibrinolysis and its regulation. They express receptors for plasminogen activators and produce tissuetype plasminogen activator. Through local generation of plasmin, the normal endothelial monolayer can promote the lysis of nascent thrombi. When activated by inflammatory cytokines—bacterial endotoxin, or angiotensin II, for example—endothelial cells can produce substantial quantities of the major inhibitor of fibrinolysis, plasminogen activator inhibitor 1 (PAI-1). Thus, under pathologic circumstances, the endothelial cell may promote local thrombus accumulation rather than combat it. Inflammatory stimuli also induce the expression of the potent procoagulant tissue factor, a contributor to disseminated intravascular coagulation in sepsis. Endothelial cells also participate in the pathophysiology of a number of immune-mediated diseases. Lysis of endothelial cells mediated by complement provides an example of immunologically mediated tissue injury.

Presentation of foreign histocompatibility complex antigens by endothelial cells in solid organ allografts can trigger immunologic rejection. In addition, immune-mediated endothelial injury may contribute in some patients with thrombotic thrombocytopenic purpura and in patients with hemolytic uremic syndrome. Thus, in addition to contributing to innate immune responses, endothelial cells participate actively in both humoral and cellular limbs of the immune response. Endothelial cells can also regulate growth of the subjacent smooth-muscle cells. Heparan sulfate glycosaminoglycans elaborated by endothelial cells can hold smooth-muscle proliferation in check. In contrast, when exposed to various injurious stimuli, endothelial cells can elaborate growth factors and chemoattractants, such as platelet-derived growth factor, that can promote the migration and proliferation of vascular smooth-muscle cells. Dysregulated elaboration of these growth-stimulatory molecules may promote smooth-muscle accumulation in arterial hyperplastic diseases, including atherosclerosis and in-stent stenosis. Clinical Assessment of Endothelial Function Endothelial function can be assessed noninvasively and invasively, and typically involves evaluating one measure of endothelial behavior in vivo, viz., endotheliumdependent vasodilation. Using either pharmacologic or mechanical agonists, the endothelium is stimulated to release acutely molecular effectors that alter underlying smooth-muscle cell tone. Invasively, endothelial function can be assessed with the use of agonists that stimulate release of endothelial NO, such as the cholinergic agonists acetylcholine and methacholine. The typical approach involves measuring quantitatively the change in coronary diameter in response to an intracoronary infusion of these short-lived, rapidly acting agents. Noninvasively, endothelial function can be assessed in the forearm circulation by performing occlusion of brachial artery blood flow with a blood pressure cuff, after which the cuff is deflated and the change in brachial artery blood flow and diameter are measured ultrasonographically (Fig. 1-2). This approach depends upon shear stress-dependent changes in endothelial release of NO following restoration of blood flow, as well as the effect of adenosine released (transiently) from ischemic tissue in the forearm. Typically, the change in vessel diameter detected by these invasive and noninvasive approaches is ∼10%. In individuals with frank atherosclerosis or risk factors for atherosclerosis (especially hypertension, hypercholesterolemia, diabetes mellitus, and smoking), such studies can detect endothelial dysfunction as defined by a smaller change in diameter and, in the extreme case, a so-called paradoxical vasoconstrictor response owing to the direct effect of cholinergic agonists on vascular smooth-muscle cell tone.

CHAPTER 1

smooth-muscle cells at the level of the muscular arteries 5 controls blood pressure and, hence, regional blood flow and the afterload experienced by the left ventricle (see later). The vasomotor tone of veins, governed by smooth-muscle cell tone, regulates the capacitance of the venous tree and influences the preload experienced by both ventricles. Smooth-muscle cells in the adult vessel seldom replicate. This homeostatic quiescence of smooth-muscle cells changes under conditions of arterial injury or inflammatory activation. Proliferation and migration of arterial smooth-muscle cells can contribute to the development of arterial stenoses in atherosclerosis, of arteriolar remodeling that can sustain and propagate hypertension, and of the hyperplastic response of arteries injured by angioplasty or stent deployment. In the pulmonary circulation, smooth-muscle migration and proliferation contribute decisively to the pulmonary vascular disease that gradually occurs in response to sustained high-flow states, such as left-to-right shunts. Such pulmonary vascular disease provides a major obstacle to the management of many patients with adult congenital heart disease. Smooth-muscle cells also secrete the bulk of vascular extracellular matrix. Excessive production of collagen and glycosaminoglycans contributes to the remodeling and altered biology and biomechanics of arteries affected by hypertension or atherosclerosis. In larger elastic arteries, the elastin synthesized by smooth-muscle cells serves to maintain not only normal arterial structure but also hemodynamic function.The ability of the larger arteries, such as the aorta, to store the kinetic energy of systole promotes tissue perfusion during diastole. Arterial stiffness associated with aging or disease, as manifested by a widening pulse pressure, increases left ventricular afterload and portends a poor prognosis. Like endothelial cells, vascular smooth-muscle cells do not merely respond to vasomotor or inflammatory stimuli elaborated by other cell types but can themselves serve as a source of such stimuli. For example, when stimulated by bacterial endotoxin, smooth-muscle cells can elaborate large quantities of proinflammatory cytokines, such as interleukin 6, as well as lesser quantities of many other proinflammatory mediators. Like endothelial cells, upon inflammatory activation, arterial smooth-muscle cells can produce prothrombotic mediators, such as tissue factor, the antifibrinolytic protein PAI-1, and other molecules that modulate thrombosis and fibrinolysis. Smooth-muscle cells may also elaborate autocrine growth factors that can amplify hyperplastic responses to arterial injury.

Basic Biology of the Cardiovascular System

FIGURE 1-2 Assessment of endothelial function in vivo using blood pressure cuff-occlusion and release. Upon deflation of the cuff, changes in diameter (A) and blood flow (B) of the brachial artery are monitored with an ultrasound probe (C). (Reproduced with permission of J. Vita, MD.)

VASCULAR SMOOTH-MUSCLE CELL

Vascular Smooth-Muscle Cell Function

The vascular smooth-muscle cell, the major cell type of the media layer of blood vessels, also actively contributes to vascular pathobiology. Contraction and relaxation of

A principal function of vascular smooth-muscle cells is to maintain vessel tone. Vascular smooth-muscle cells contract when stimulated by a rise in intracellular calcium

6

NE, ET-1, AngII

NO

SECTION I

VDCC PIP2

PLC

K+ Ch

Na-K ATPase

G

GTP

AC ATP

SR

RhoA

Introduction to Cardiovascular Disorders

IP3R RyrR

IP3

G

pGC sGC

DAG

BetaAgonist

ANP

Plb ATPase

cGMP

cAMP

PKG

PKA

Calcium

PKC Rho Kinase

MLCK

Caldesmon Calponin

MLCP

FIGURE 1-3 Regulation of vascular smooth-muscle cell calcium concentration and actomyosin ATPase-dependent contraction. NE, norepinephrine; ET-1, endothelin-1; AngII, angiotensin II; PIP2, phosphatidylinositol 4,5-biphosphate; PLC, phospholipase C; DAG, diacylglycerol; G, G-protein; VDCC, voltage-dependent calcium channel; IP3, inositol 1,4,5-trisphosphate; PKC, protein kinase C; SR, sarcoplasmic

reticulum; NO, nitric oxide; ANP, antrial natriuretic peptide; pGC, particular guanylyl cyclase; AC, adenylyl cyclase; sGC, soluble guanylyl cyclase; PKG, protein kinase G; PKA, protein kinase A; MLCK, myosin light chain kinase; MLCP, myosin light chain phosphatase. (Modified from B Berk, in Vascular Medicine, 3d ed, p 23. Philadelphia, Saunders, Elsevier, 2006; with permission.)

concentration by calcium influx through the plasma membrane and by calcium release from intracellular stores (Fig. 1-3). In vascular smooth-muscle cells, voltagedependent L-type calcium channels open with membrane depolarization, which is regulated by energy-dependent ion pumps such as the Na+,K+-ATPase and ion channels such as the Ca2+-sensitive K+ channel. Local changes in intracellular calcium concentration, termed calcium sparks, result from the influx of calcium through the voltagedependent calcium channel and are caused by the coordinated activation of a cluster of ryanodine-sensitive calcium release channels in the sarcoplasmic reticulum (see later). Calcium sparks lead to a further direct increase in intracellular calcium concentration and indirectly increases intracellular calcium concentration by activating chloride channels. In addition, calcium sparks reduce contractility by activating large-conductance calciumsensitive K+ channels, hyperpolarizing the cell membrane and thereby limiting further voltage-dependent increases in intracellular calcium.

Biochemical agonists also increase intracellular calcium concentration, doing so by receptor-dependent activation of phospholipase C with hydrolysis of phosphatidylinositol 4,5-bisphosphate with generation of diacylglycerol (DAG) and inositol 1,4,5-trisphosphate (IP3). These membrane lipid derivatives, in turn, activate protein kinase C and increase intracellular calcium concentration. In addition, IP3 binds to its specific receptor found in the sarcoplasmic reticulum membrane to increase calcium efflux from this calcium storage pool into the cytoplasm. Vascular smooth-muscle cell contraction is principally controlled by the phosphorylation of myosin light chain, which, in the steady state, depends on the balance between the actions of myosin light chain kinase and myosin light chain phosphatase. Myosin light chain kinase is activated by calcium through the formation of a calcium-calmodulin complex; with phosphorylation of myosin light chain by this kinase, the myosin ATPase activity is increased and contraction sustained. Myosin light chain phosphatase dephosphorylates myosin light

Vascular smooth-muscle cell tone is governed by the autonomic nervous system and by the endothelium in tightly regulated control networks. Autonomic neurons enter the blood vessel media from the adventitia and modulate vascular smooth-muscle cell tone in response to baroreceptors and chemoreceptors within the aortic arch and carotid bodies, and in response to thermoreceptors in the skin. These regulatory components comprise rapidly acting reflex arcs modulated by central inputs that respond to sensory inputs (olfactory, visual, auditory, and tactile) as well as emotional stimuli. Autonomic regulation of vascular tone is mediated by three classes of nerves: sympathetic, whose principal neurotransmitters are epinephrine and norepinephrine; parasympathetic, whose principal neurotransmitter is acetylcholine; and nonadrenergic/noncholinergic, which include two subgroups—nitrergic, whose principal neurotransmitter

Basic Biology of the Cardiovascular System

Control of Vascular Smooth-Muscle Cell Tone

is NO; and peptidergic, whose principal neurotransmitters 7 are substance P, vasoactive intestinal peptide, calcitonin gene-related peptide, and ATP. Each of these neurotransmitters acts through specific receptors on the vascular smooth-muscle cell to modulate intracellular calcium and, consequently, contractile tone. Norepinephrine activates α receptors and epinephrine activates α and β receptors (adrenergic receptors); in most blood vessels, norepinephrine activates postjunctional α1 receptors in large arteries, and α2 receptors in small arteries and arterioles, leading to vasoconstriction. Most blood vessels express β2 adrenergic receptors on their vascular smooth-muscle cells and respond to β agonists by cyclic AMP–dependent relaxation. Acetylcholine released from parasympathetic neurons binds to muscarinic receptors (of which there are five subtypes, M1–M5) on vascular smooth-muscle cells to yield vasorelaxation. In addition, NO stimulates presynaptic neurons to release acetylcholine, which can stimulate release of NO from the endothelium. Nitrergic neurons release NO produced by neuronal NO synthase, which causes vascular smooth-muscle cell relaxation via the cyclic GMP–dependent and –independent mechanisms described above. The peptidergic neurotransmitters all potently vasodilate, acting either directly or through endothelium-dependent NO release to decrease vascular smooth-muscle cell tone. The endothelium modulates vascular smooth-muscle tone by the direct release of several effectors, including NO, prostacyclin, and endothelium-derived hyperpolarizing factor, all of which cause vasorelaxation; and endothelin, which causes vasoconstriction.The release of these endothelial effectors of vascular smooth-muscle cell tone is stimulated by mechanical (shear stress, cyclic strain, etc.) and biochemical mediators (purinergic agonists, muscarinic agonists, peptidergic agonists), with the biochemical mediators acting through endothelial receptors specific to each class. In addition to these local, paracrine modulators of vascular smooth-muscle cell tone, circulating mediators can also affect tone, including norepinephrine and epinephrine, vasopressin, angiotensin II, bradykinin, and the natriuretic peptides (ANP, BNP, CNP, and DNP), as discussed above.

CHAPTER 1

chain, reducing myosin ATPase activity and contractile force. Phosphorylation of the myosin binding subunit (thr695) of myosin light chain phosphatase by Rho kinase inhibits phosphatase activity and induces calcium sensitization of the contractile apparatus. Rho kinase is itself activated by the small GTPase RhoA, which is stimulated by guanosine exchange factors and inhibited by GTPase-activating proteins. Both cyclic AMP and cyclic GMP relax vascular smooth-muscle cells, doing so by complex mechanisms. β-Agonists acting through their G-protein-coupled receptors activate adenylyl cyclase to convert ATP to cyclic AMP; NO and atrial natriuretic peptide acting directly and via a G-protein-coupled receptor, respectively, activate guanylyl cyclase to convert GTP to cyclic GMP. These agents, in turn, activate protein kinase A and protein kinase G, respectively, which inactivates myosin light chain kinase and decreases vascular smoothmuscle cell tone. In addition, protein kinase G can directly interact with the myosin-binding substrate subunit of myosin light chain phosphatase, increasing phosphatase activity and decreasing vascular tone. Lastly, several mechanisms drive NO-dependent, protein kinase G–mediated reductions in vascular smooth-muscle cell calcium concentration, including phosphorylationdependent inactivation of RhoA; decreased IP3 formation; phosphorylation of the IP3 receptor–associated cyclic GMP kinase substrate, with subsequent inhibition of IP3 receptor function; phosphorylation of phospholamban, which increases calcium ATPase activity and sequestration of calcium in the sarcoplasmic reticulum; and protein kinase G–dependent stimulation of plasma membrane calcium ATPase activity, perhaps by activation of the Na+,K+-ATPase or hyperpolarization of the cell membrane by activation of calcium-dependent K+ channels.

VASCULAR REGENERATION Growing new blood vessels can occur in response to conditions such as chronic hypoxia or tissue ischemia. Growth factors, including vascular endothelial growth factor, activate a signaling cascade that stimulates endothelial proliferation and tube formation, defined as angiogenesis. The development of collateral vascular networks in the ischemic myocardium reflects this process and can result from selective activation of endothelial progenitor cells, which may reside in the blood vessel wall or home

8 to the ischemic tissue subtended by an occluded or

SECTION I

severely stenotic vessel from the bone marrow. True arteriogenesis, or the development of a new blood vessel comprising all three cell layers, does not normally occur in the cardiovascular system of mammals. Recent insights into the molecular determinants and progenitor cells that can recapitulate blood vessel development de novo is the subject of ongoing and rapidly advancing study.

Introduction to Cardiovascular Disorders

VASCULAR PHARMACOGENOMICS The past decade has witnessed considerable progress in efforts to define genetic differences underlying individual differences in vascular pharmacologic responses. Many investigators have focused on receptors and enzymes associated with neurohumoral modulation of vascular function, as well as hepatic enzymes that metabolize drugs affecting vascular tone.The genetic polymorphisms thus far associated with differences in vascular response often (but not invariably) relate to functional differences in the activity or expression of the receptor or enzyme of interest. Some of these polymorphisms appear to be differentially expressed in specific ethnic groups or by sex. A summary of recently identified polymorphisms defining these vascular pharmacogenomic differences is provided in Table 1-2.

CELLULAR BASIS OF CARDIAC CONTRACTION THE CARDIAC ULTRASTRUCTURE About three-fourths of the ventricle is composed of individual striated muscle cells (myocytes), normally 60–140 µm in length and 17–25 µm in diameter (Fig. 1-4A). Each cell contains multiple, rodlike crossbanded strands (myofibrils) that run the length of the cell and are, in turn, composed of serially repeating structures, the sarcomeres. The cytoplasm between the myofibrils contains other cell constituents, including the single centrally located nucleus, numerous mitochondria, and the intracellular membrane system, the sarcoplasmic reticulum. The sarcomere, the structural and functional unit of contraction, lies between two adjacent dark lines, the Z lines. The distance between Z lines varies with the degree of contraction or stretch of the muscle and ranges between 1.6 and 2.2 µm. Within the confines of the sarcomere are alternating light and dark bands, giving the myocardial fibers their striated appearance under the light microscope. At the center of the sarcomere is a dark band of constant length (1.5 µm), the A band, which is flanked by two lighter bands, the I bands, which are of variable length. The sarcomere of heart

TABLE 1-2 GENETIC POLYMORPHISMS IN VASCULAR FUNCTION AND DISEASE RISK GENE

POLYMORPHIC ALLELE

CLINICAL IMPLICATIONS

α-adrenergic receptors α-1A α-2B α-2C

Arg492Cys Glu9/G1712 A2cDcl3232-325

Angiotensin-converting enzyme (ACE)

Insertion/deletion polymorphism in intron 16

Ang II type I receptor

1166A → C Ala-Cys

None Increased CHD events Ethnic differences in risk of hypertension or heart failure D allele or DD genotype–increased response to ACE inhibitors; inconsistent data for increased risk of atherosclerotic heart disease, and hypertension Increased response to Ang II and increased risk of pregnancy-associated hypertension

β-Adrenergic receptors β-1 β-2

B2-Bradykinin receptor Endothelial nitric oxide synthase (eNOS)

Ser49Gly Arg389Gly

Increased HR and DCM risk Increased heart failure in blacks

Arg16Gly Glu27Gln Thr164Ile Cys58Thr, Cys412Gly, Thr21Met Nucleotide repeats in introns 4 and 13, Glu298Asp Thr785Cys

Familial hypertension, increased obesity risk Hypertension in white type II diabetics Decreased agonist affinity and worse HF outcome Increased risk of hypertension in some ethnic groups Increased MI and venous thrombosis Early coronary artery disease

Note: CHD, coronary heart disease; HR, heart rate; DCM, dilated cardiomyopathy; HF, heart failure; MI, myocardial infarction. Source: Adapted From B Schaefer et al: Heart Dis 5:129, 2003.

9 MYOFIBER

CHAPTER 1

A 10 ␮m

Myocyte Ca2⫹ enters Ca2⫹ pump Ca2⫹ ‘trigger’ MYOFIBRIL

SR

Ca2⫹ leaves

MYOFIBRIL

CH MITOON DR ION

MYOCYT

E

T-tubule

FREE Ca2ⴙ SR Contract Relax Systole

MYOFIBRIL

B

Z

C

Diastole

Head Titin Myosin Z D

Actin

M

FIGURE 1-4 A shows the branching myocytes making up the cardiac myofibers. B illustrates the critical role played by the changing [Ca2+] in the myocardial cytosol. Ca2+ ions are schematically shown as entering through the calcium channel that opens in response to the wave of depolarization that travels along the sarcolemma. These Ca2+ ions “trigger” the release of more calcium from the sarcoplasmic reticulum (SR) and thereby initiate a contraction-relaxation cycle. Eventually the

muscle, like that of skeletal muscle, consists of two sets of interdigitating myofilaments. Thicker filaments, composed principally of the protein myosin, traverse the A band. They are about 10 nm (100 Å) in diameter, with tapered ends. Thinner filaments, composed primarily of actin, course from the Z line through the I band into the A band. They are approximately 5 nm (50 Å) in diameter and 1.0 µm in length. Thus, thick and thin filaments overlap only within the (dark) A band, while the (light) I band contains only thin filaments. On

43 nm

small quantity of Ca2+ that has entered the cell leaves predominantly through an Na+/Ca2+ exchanger, with a lesser role for the sarcolemmal Ca2+ pump. The varying actin-myosin overlap is shown for (B) systole, when [Ca2+] is maximal, and (C) diastole, when [Ca2+] is minimal. D. The myosin heads, attached to the thick filaments, interact with the thin actin filaments. (From LH Opie, Heart Physiology, reprinted with permission. Copyright LH Opie, 2004.)

electron-microscopic examination, bridges may be seen to extend between the thick and thin filaments within the A band; these comprise myosin heads (see later) bound to actin filaments.

THE CONTRACTILE PROCESS The sliding filament model for muscle contraction rests on the fundamental observation that both the thick and thin filaments are constant in overall length during both

Basic Biology of the Cardiovascular System

Na⫹ exchange

10 contraction and relaxation. With activation, the actin

SECTION I Introduction to Cardiovascular Disorders

filaments are propelled further into the A band. In the process, the A band remains constant in length, whereas the I band shortens and the Z lines move toward one another. The myosin molecule is a complex, asymmetric fibrous protein with a molecular mass of about 500,000 Da; it has a rodlike portion that is about 150 nm (1500 Å) in length with a globular portion (head) at its end. These globular portions of myosin form the bridges between the myosin and actin molecules and are the site of ATPase activity. In forming the thick myofilament, which is composed of ∼300 longitudinally stacked myosin molecules, the rodlike segments of the myosin molecules are laid down in an orderly, polarized manner, leaving the globular portions projecting outward so that they can interact with actin to generate force and shortening (Fig. 1-4B).

Actin has a molecular mass of about 47,000 Da. The thin filament consists of a double helix of two chains of actin molecules wound about each other on a larger molecule, tropomyosin. A group of regulatory proteins— troponins C, I, and T—are spaced at regular intervals on this filament (Fig. 1-5). In contrast to myosin, actin lacks intrinsic enzymatic activity but does combine reversibly with myosin in the presence of ATP and Ca2+. The calcium ion activates the myosin ATPase, which in turn breaks down ATP, the energy source for contraction (Fig. 1-5). The activity of myosin ATPase determines the rate of forming and breaking of the actomyosin cross-bridges and, ultimately, the velocity of muscle contraction. In relaxed muscle, tropomyosin inhibits this interaction. Titin (Fig. 1-4D) is a large, flexible, myofibrillar protein that connects myosin to the Z line. Its stretching contributes to the elasticity of the heart.

ADP

ATP

Pi

1. ATP hydrolysis

Relaxed

Relaxed, energized Actin

A 4. Dissociation of actin and myosin

B

ATP

Actin

2. Formation of active complex Pi

ADP

ADP

3. Product dissociation Active complex

Rigor complex

C

FIGURE 1-5 Four steps in cardiac muscle contraction and relaxation. In relaxed muscle (A), ATP bound to the myosin cross-bridge dissociates the thick and thin filaments. Step 1: Hydrolysis of myosin-bound ATP by the ATPase site on the myosin head transfers the chemical energy of the nucleotide to the activated cross-bridge (B). When cytosolic Ca2+ concentration is low, as in relaxed muscle, the reaction cannot proceed because tropomyosin and the troponin complex on the thin filament do not allow the active sites on actin to interact with the cross-bridges. Therefore, even though the cross-bridges are energized, they cannot interact with actin. Step 2: When Ca2+ binding to troponin C has exposed active sites on the thin filament, actin interacts with the myosin cross-bridges to form an active complex (D) in which the energy derived from ATP is retained in the actin-bound cross-bridge, whose orientation has not yet shifted.

D

Step 3: The muscle contracts when ADP dissociates from the cross-bridge. This step leads to the formation of the lowenergy rigor complex (C) in which the chemical energy derived from ATP hydrolysis has been expended to perform mechanical work (the “rowing” motion of the cross-bridge). Step 4: The muscle returns to its resting state, and the cycle ends when a new molecule of ATP binds to the rigor complex and dissociates the cross-bridge from the thin filament. This cycle continues until calcium is dissociated from troponin C in the thin filament, which causes the contractile proteins to return to the resting state with the cross-bridge in the energized state. ATP, adenosine triphosphate; ATPase, adenosine triphosphatase; ADP, adenosine disphosphate. [From AM Katz: Heart failure: Cardiac function and dysfunction, in Atlas of Heart Diseases, 3d ed, WS Colucci (ed). Philadelphia, Current Medicine, 2002. Reprinted with permission.]

In the inactive state, the cardiac cell is electrically polarized, i.e., the interior has a negative charge relative to the outside of the cell, with a transmembrane potential of –80 to –100 mV (Chap. 14).The sarcolemma, which in the resting state is largely impermeable to Na+, has a Na+- and K+-stimulating pump energized by ATP that extrudes Na+ from the cell; this pump plays a critical role in establishing the resting potential. Thus, intracellular [K+] is

␤

␥

␣s

SL

Adenyl cyclase

␤

receptor

11

Ca2⫹

P

GTP

⫹

Ca2⫹

⫹

cAMP

SR

Via protein kinase A

P

Metabolism • glycolysis • lipolysis • citrate cycle

Ca2⫹ ADP ⫹ Pi

⫹

ATP

troponin C

⫹

Myosin ATPase

2

ADP ⫹ Pi ⫹

cAMP via PL

INCREASED 1. rate of contraction 2. peak force 3. rate of relaxation

1

3

⫹ Control

Force

␤

cAMP via TnI

Time Pattern of contraction

FIGURE 1-6 Signal systems involved in positive intropic and lusitropic (enhanced relaxation) effects of a-adrenergic stimulation. When the β-adrenergic agonist interacts with the β receptor, a series of G-protein–mediated changes leads to activation of adenylyl cyclase and formation of cyclic adenosine monophosphate (cAMP). The latter acts via protein kinase A to stimulate metabolism (left) and to phosphorylate the Ca2+ channel protein (right). The result is an enhanced opening probability of the Ca2+ channel, thereby increasing the inward movement of Ca2+ ions through the sarcolemma (SL) of the T tubule. These Ca2+ ions release more calcium from the sarcoplasmic reticulum (SR) to increase cytosolic Ca2+ and to activate troponin C. Ca2+ ions also increase the rate of breakdown of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) and inorganic phosphate (Pi). Enhanced myosin ATPase activity explains the increased rate of contraction, with increased activation of troponin C explaining increased peak force development. An increased rate of relaxation is explained because cAMP also activates the protein phospholamban, situated on the membrane of the SR, that controls the rate of uptake of calcium into the SR. The latter effect explains enhanced relaxation (lusitropic effect). P, phosphorylation; PL, phospholamban; TnI, troponin I. (Modified from LH Opie, Heart Physiology, reprinted with permission. Copyright LH Opie, 2004.)

Basic Biology of the Cardiovascular System

CARDIAC ACTIVATION

␤ - ADRENERGIC AGONIST

CHAPTER 1

During activation of the cardiac myocyte, Ca2+ becomes attached to troponin C, which results in a conformational change in the regulatory protein tropomyosin; the latter, in turn, exposes the actin cross-bridge interaction sites (Fig. 1-5). Repetitive interaction between myosin heads and actin filaments is termed cross-bridge cycling, which results in sliding of the actin along the myosin filaments, ultimately causing muscle shortening and/or the development of tension.The splitting of ATP then dissociates the myosin cross-bridge from actin. In the presence of ATP (Fig. 1-5), linkages between actin and myosin filaments are made and broken cyclically as long as sufficient Ca2+ is present; these linkages cease when [Ca2+] falls below a critical level, and the troponin-tropomyosin complex once more prevents interactions between the myosin cross-bridges and actin filaments (Fig. 1-6). Intracytoplasmic Ca2+ is a principal mediator of the inotropic state of the heart. The fundamental action of most agents that stimulate myocardial contractility (positive inotropic stimuli), including the digitalis glycosides and β-adrenergic agonists, is to raise the [Ca2+] in the vicinity of the myofilaments, which, in turn, triggers cross-bridge cycling. Increased impulse traffic in the cardiac adrenergic nerves stimulates myocardial contractility as a consequence of the release of norepinephrine from cardiac adrenergic nerve endings. Norepinephrine activates myocardial β receptors and, through the Gs-stimulated guanine nucleotide binding protein, activates the enzyme adenylyl cyclase, which leads to the formation of the intracellular second messenger cyclic AMP from ATP (Fig. 1-6). Cyclic AMP, in turn, activates protein kinase A (PKA), which phosphorylates the Ca2+ channel in the myocardial sarcolemma, thereby enhancing the influx of Ca2+ into the myocyte. Other functions of PKA are discussed below. The sarcoplasmic reticulum (SR) (Fig. 1-7) is a complex network of anastomosing intracellular channels that invests the myofibrils. Its longitudinally disposed membrane-lined tubules closely invest the surfaces of individual sarcomeres but have no direct continuity with the outside of the cell. However, closely related to the SR, both structurally and functionally, are the transverse tubules, or T system, formed by tubelike invaginations of the sarcolemma that extend into the myocardial fiber along the Z lines, i.e., the ends of the sarcomeres.

12

Na⫹/Ca2⫹ Plasma membrane exchanger Ca2⫹ pump T tubule

B1

Na⫹ pump

B2

Extracellular

SECTION I

Plasma membrane Intracellular (cytosol)

Plasma membrane Ca2⫹ A channel

Ca2⫹release channel (“foot” protein)

Introduction to Cardiovascular Disorders

A1

Cisterna Sarcoplasmic reticulum

Sarcotubular network

G Calsequestrin

Sarcoplasmic reticulum Ca2⫹ pump Mitochondria

C

D

H

E

Z-line

F

Troponin C

Thin filament

Contractile proteins

Thick filament

FIGURE 1-7 The Ca2+ fluxes and key structures involved in cardiac excitation-contraction coupling. The arrows denote the direction of Ca2+ fluxes. The thickness of each arrow indicates the magnitude of the calcium flux. Two Ca2+ cycles regulate excitation-contraction coupling and relaxation. The larger cycle is entirely intracellular and involves Ca2+ fluxes into and out of the sarcoplasmic reticulum, as well as Ca 2+ binding to and release from troponin C. The smaller extracellular Ca2+ cycle occurs when this cation moves into and out of the cell. The action potential opens plasma membrane Ca2+ channels to allow passive entry of Ca2+ into the cell from the extracellular fluid (arrow A). Only a small portion of the Ca2+ that enters the cell directly activates the contractile proteins (arrow A1). The extracellular cycle is completed when Ca2+ is actively transported back out to the extracellular fluid by way of two plasma membrane fluxes mediated by the sodium-calcium exchanger (arrow B1) and the plasma membrane calcium pump (arrow B2). In the intracellular Ca2+ cycle, passive Ca2+ release occurs through channels in the cisternae (arrow C) and initiates contraction; active Ca2+ uptake by the Ca2+ pump of the sarcotubular network (arrow D) relaxes the heart. Diffusion of Ca2+ within the sarcoplasmic reticulum (arrow G) returns this activator cation to the cisternae, where it is stored in a complex with calsequestrin and other calcium-binding proteins. Ca2+ released from the sarcoplasmic reticulum initiates systole when it binds to troponin C (arrow E). Lowering of cytosolic [Ca2+] by the sarcoplasmic reticulum (SR) cause this ion to dissociate from troponin (arrow F) and relaxes the heart. Ca2+ may also move between mitochondria and cytoplasm (H). (Adapted from Katz, with permission.)

relatively high and [Na+] is far lower, while, conversely, extracellular [Na+] is high and [K+] is low. At the same time, in the resting state, extracellular [Ca2+] greatly exceeds free intracellular [Ca2+]. The four phases of the action potential are illustrated in Fig. 14-1B. During the plateau of the action potential (phase 2), there is a slow inward current through L-type Ca2+ channels in the sarcolemma (Fig. 1-7).The depolarizing current not only extends across the surface of the cell but penetrates deeply into the cell by way of the ramifying T tubular system. The absolute quantity of Ca2+ that crosses the sarcolemma and T system is relatively small and itself appears to be insufficient to bring about full activation of the contractile apparatus. However, this Ca2+ current triggers the release of much larger quantities of Ca2+ from the SR, a process termed Ca2+-induced Ca2+ release. The latter is a major determinant of intracytoplasmic [Ca2+] and therefore of myocardial contractility. Ca2+ is released from the SR through a Ca2+ release channel, a cardiac isoform of the ryanodine receptor (RyR2), which controls intracytoplasmic [Ca2+] and, as in vascular smooth-muscle cells, leads to the local changes in intracellular [Ca2+] called calcium sparks. A number of regulatory proteins, including calstabin 2, inhibit RyR2 and, thereby, the release of Ca2+ from the SR. PKA dissociates calstabin from the RyR2, enhancing Ca2+ release and, thereby, myocardial contractility. Excessive plasma catecholamine levels and cardiac sympathetic neuronal release of norepinephrine cause hyperphosphorylation of PKA, leading to calstabin 2–depleted RyR2. The latter depletes SR Ca2+ stores and, thereby, impairs cardiac contraction, leading to heart failure, and also triggers ventricular arrhythmias. The Ca2+ released from the SR then diffuses toward the myofibrils, where, as already described, it combines with troponin C (Fig. 1-6). By repressing this inhibitor of contraction, Ca2+ activates the myofilaments to shorten. During repolarization, the activity of the Ca2+ pump in the SR, the SR Ca2+ ATPase (SERCA2A), reaccumulates Ca2+ against a concentration gradient, and the Ca2+ is stored in the SR by its attachment to a protein, calsequestrin.This reaccumulation of Ca2+ is an energy (ATP) requiring process that lowers the cytoplasmic [Ca2+] to a level that inhibits the actomyosin interaction responsible for contraction and in this manner leads to myocardial relaxation. Also, there is an exchange of Ca2+ for Na+ at the sarcolemma (Fig. 1-7), reducing the cytoplasmic [Ca2+]. Cyclic AMP–dependent PKA phosphorylates the SR protein phospholamban; the latter, in turn, permits activation of the Ca2+ pump, thereby increasing the uptake of Ca2+ by the SR, accelerating the rate of relaxation and providing larger quantities of Ca2+ in the SR for release by subsequent depolarization, thereby stimulating contraction. Thus, the combination of the cell membrane, transverse tubules, and SR, with their ability to transmit the

CONTROL OF CARDIAC PERFORMANCE AND OUTPUT

TABLE 1-3 DETERMINANTS OF STROKE VOLUME I. Ventricular Preload A. Blood volume B. Distribution of blood volume 1. Body position 2. Intrathoracic pressure 3. Intrapericardial pressure 4. Venous tone 5. Pumping action of skeletal muscles C. Atrial contraction II. Ventricular Afterload A. Systemic vascular resistance B. Elasticity of arterial tree C. Arterial blood volume D. Ventricular wall tension 1. Ventricular radius 2. Ventricular wall thickness III. Myocardial Contractilitya A. Intramyocardial [Ca2+] ↑↓ B. Cardiac adrenergic nerve activity ↑↓b C. Circulating catecholamines ↑↓b D. Cardiac rate ↑↓b E. Exogenous inotropic agents ↑ F. Myocardial ischemia ↓ G. Myocardial cell death (necrosis, apoptosis, autophagy) ↓ H. Alterations of sarcomeric and cytoskeletal proteins ↓ 1. Genetic 2. Hemodynamic overload I. Myocardial fibrosis ↓ J. Chronic overexpression of neurohormones ↓ K. Ventricular remodeling ↓ L. Chronic and/or excessive myocardial hypertrophy ↓ a

Arrows indicate directional effects of determinants of contractility. Contractility rises initially but later becomes depressed.

b

The preload determines the length of the sarcomeres at the onset of contraction. The length of the sarcomeres associated with the most forceful contraction is ∼2.2 µm. At this length, the two sets of myofilaments are configured so as to provide the greatest area for their interaction. The length of the sarcomere also regulates the extent of activation of the contractile system, i.e., its sensitivity to Ca2+. According to this concept, termed length-dependent activation, the myofilament sensitivity to Ca2+ is also maximal at the optimal sarcomere length. The relation between the initial length of the muscle fibers and the developed force has prime importance for the function of heart muscle.This relationship forms the basis of Starling’s law of the heart, which states that, within limits, the force of ventricular contraction depends on the end-diastolic length of the cardiac muscle; in the intact heart the latter relates closely to the ventricular end-diastolic volume. Cardiac Performance The ventricular end-diastolic or “filling” pressure is sometimes used as a surrogate for the end-diastolic volume. In isolated heart and heart-lung preparations, the stroke volume varies directly with the end-diastolic fiber length (preload) and inversely with the arterial resistance (afterload), and as the heart fails—i.e., as its contractility declines—it delivers a progressively smaller stroke volume from a normal or even elevated end-diastolic volume.The relation between the ventricular end-diastolic pressure and the stroke work of the ventricle (the ventricular function curve) provides a useful definition of the level of contractility of the heart in the intact organism. An increase in contractility is accompanied by a shift of the ventricular function curve upward and to the left (greater stroke work at any level of ventricular end-diastolic pressure, or lower end-diastolic volume at any level of stroke work), while a shift downward and to the right characterizes depression of contractility (Fig. 1-8). Ventricular Afterload In the intact heart, as in isolated cardiac muscle, the extent (and velocity) of shortening of ventricular muscle fibers at any level of preload and of myocardial contractility relate inversely to the afterload, i.e., the load that opposes shortening. In the intact heart, the afterload may be defined as the tension developed in the ventricular wall during ejection. Afterload is determined by the aortic pressure as well as by the volume and thickness of the ventricular cavity. Laplace’s law indicates that the tension of the myocardial fiber is a function of the product of the intracavitary ventricular pressure and ventricular radius divided by the wall thickness.

13

Basic Biology of the Cardiovascular System

The extent of shortening of heart muscle and, therefore, the stroke volume of the ventricle in the intact heart depend on three major influences: (1) the length of the muscle at the onset of contraction, i.e., the preload; (2) the tension that the muscle is called upon to develop during contraction, i.e., the afterload; and (3) the contractility of the muscle, i.e., the extent and velocity of shortening at any given preload and afterload.The major determinants of preload, afterload, and contractility are shown in Table 1-3.

The Role of Muscle Length (Preload)

CHAPTER 1

action potential and to release and then reaccumulate Ca2+, play a fundamental role in the rhythmic contraction and relaxation of heart muscle. Genetic or pharmacologic alterations of any component, whatever its etiology, can disturb these functions.

14

Maximal activity

2

1

SECTION I Introduction to Cardiovascular Disorders

Ventricular performance

Normal-exercise

C

Venous return

Preload

Normal-rest Contractility

Contractile state of myocardium Walking B

Stroke volume Cardiac output

Afterload

Peripheral resistance

3 3′ D

Rest

Exercise Heart failure

A E 4

Dyspnea

Arterial pressure

Heart rate

Fatal myocardial depression

Pulm. edema Ventricular EDV

Medullary vasomotor and cardiac centers

Carotid and aortic pressoreceptors

Higher nervous centers

Stretching of myocardium

FIGURE 1-8 The interrelations among influences on ventricular end-diastolic volume (EDV) through stretching of the myocardium and the contractile state of the myocardium. Levels of ventricular EDV associated with filling pressures that result in dyspnea and pulmonary edema are shown on the abscissa. Levels of ventricular performance required when the subject is at rest, while walking, and during maximal activity are designated on the ordinate. The broken lines are the descending limbs of the ventricular-performance curves, which are rarely seen during life but show the level of ventricular performance if end-diastolic volume could be elevated to very high levels. For further explanation, see text. [Modified from WS Colucci and E Braunwald: Pathophysiology of Heart Failure, in Braunwald’s Heart Disease, 7th ed, DP Zipes et al (eds). Philadelphia, Elsevier, 2005.]

FIGURE 1-9 Interactions in the intact circulation of preload, contractility, and afterload in producing stroke volume. Stroke volume combined with heart rate determines cardiac output, which, when combined with peripheral vascular resistance, determines arterial pressure for tissue perfusion. The characteristics of the arterial system also contribute to afterload, an increase of which reduces stroke volume. The interaction of these components with carotid and aortic arch baroreceptors provides a feedback mechanism to higher medullary and vasomotor cardiac centers and to higher levels in the central nervous system to affect a modulating influence on heart rate, peripheral vascular resistance, venous return, and contractility. [From MR Starling: Physiology of myocardial contraction, in Atlas of Heart Failure: Cardiac Function and Dysfunction, 3d ed, WS Colucci and E Braunwald (eds). Philadelphia, Current Medicine, 2002.]

Therefore, at any given level of aortic pressure, the afterload on a dilated left ventricle is higher than that on a normal-sized ventricle. Conversely, at the same aortic pressure and ventricular diastolic volume, the afterload on a hypertrophied ventricle is lower than of a normal chamber. The aortic pressure, in turn, depends on the peripheral vascular resistance, the physical characteristics of the arterial tree, and the volume of blood it contains at the onset of ejection. Ventricular afterload critically regulates cardiovascular performance (Fig. 1-9). As already noted, elevations of both preload and contractility increase myocardial fiber shortening, while increases in afterload reduce it. The extent of myocardial fiber shortening and left ventricular size determines stroke volume.An increase in arterial pressure induced by vasoconstriction, for example, augments afterload, which opposes myocardial fiber shortening, reducing stroke volume. When myocardial contractility becomes impaired and the ventricle dilates, afterload rises (Laplace’s law) and

limits cardiac output. Increased afterload may also result from neural and humoral stimuli that occur in response to a fall in cardiac output. This increased afterload may reduce cardiac output further, thereby increasing ventricular volume and initiating a vicious circle, especially in patients with ischemic heart disease and limited myocardial O2 supply. Treatment with vasodilators has the opposite effect; by reducing afterload, cardiac output rises (Chap. 17). Under normal circumstances, the various influences acting on cardiac performance enumerated above interact in a complex fashion to maintain cardiac output at a level appropriate to the requirements of the metabolizing tissues (Fig. 1-9); interference with a single mechanism may not influence the cardiac output. For example, a moderate reduction of blood volume or the loss of the atrial contribution to ventricular contraction can ordinarily be sustained without a reduction in the cardiac output at rest. Under these circumstances, other factors, such as increases in the frequency of adrenergic nerve

DIASTOLIC FUNCTION Ventricular filling is influenced by the extent and speed of myocardial relaxation, which in turn is determined by the rate of uptake of Ca2+ by the SR; the latter may be enhanced by adrenergic activation and reduced by ischemia, which reduces the ATP available for pumping Ca2+ into the SR (see earlier).The stiffness of the ventricular wall may also impede filling.Ventricular stiffness increases

Normal contractility

ASSESSMENT OF CARDIAC FUNCTION

ESPVR

Contractility

afterload LV pressure

Several techniques can define impaired cardiac function in clinical practice.The cardiac output and stroke volume may be depressed in the presence of heart failure, but, not uncommonly, these variables are within normal limits in this condition. A somewhat more sensitive index of cardiac function is the ejection fraction, i.e., the ratio of stroke volume to end-diastolic volume (normal value = 67 ± 8%), which is frequently depressed in systolic heart failure, even when the stroke volume itself is normal. Alternatively, abnormally elevated ventricular end-diastolic volume (normal value = 75 ± 20 mL/m2) or endsystolic volume (normal value = 25 ± 7 mL/m2) signify impairment of left ventricular systolic function. Noninvasive techniques, particularly echocardiography as well as radionuclide scintigraphy and cardiac MRI (Chap. 12), have great value in the clinical assessment of myocardial function.They provide measurements of enddiastolic and end-systolic volumes, ejection fraction, and systolic shortening rate, and they allow assessment of ventricular filling (see later) as well as regional contraction and relaxation.The latter measurements are particularly important in ischemic heart disease, as myocardial infarction causes regional myocardial damage.

Contractility

preload 2

A

2

1

1

3

3

LV volume

B

LV volume

FIGURE 1-10 The responses of the left ventricle to increased afterload, increased preload, and increased and reduced contractility are shown in the pressure-volume plane. A. Effects of increases in preload and afterload on the pressure-volume loop. Since there has been no change in contractility, ESPVR (the endsystolic pressure volume relation) is unchanged. With an increase in afterload, stroke volume falls (1 → 2); with an increase in preload, stroke volume rises (1 → 3). B. With increased myocardial contractility and constant LV end-diastolic volume, the ESPVR moves to the left of the normal line (lower end-systolic volume at any end-systolic pressure) and stroke volume rises (1 → 3). With reduced myocardial contractility, the ESPVR moves to the right; end-systolic volume is increased and stroke volume falls (1 → 2).

Basic Biology of the Cardiovascular System

The integrated response to exercise illustrates the interactions among the three determinants of stroke volume, i.e., preload, afterload, and contractility (Fig. 1-8). Hyperventilation, the pumping action of the exercising muscles, and venoconstriction during exercise all augment venous return and, hence, ventricular filling and preload (Table 1-3). Simultaneously, the increase in the adrenergic nerve impulse traffic to the myocardium, the increased concentration of circulating catecholamines, and the tachycardia that occur during exercise combine to augment the contractility of the myocardium (Fig. 1-8, curves 1 and 2) and together elevate stroke volume and stroke work, without a change or even a reduction of end-diastolic pressure and volume (Fig. 1-8, points A and B).Vasodilatation occurs in the exercising muscles, thus tending to limit the increase in arterial pressure that would otherwise occur as cardiac output rises to levels as high as five times greater than basal levels during maximal exercise. This vasodilatation ultimately allows the achievement of a greatly elevated cardiac output during exercise, at an arterial pressure only moderately higher than in the resting state.

LV pressure

Exercise

A limitation of measurements of cardiac output, ejec- 15 tion fraction, and ventricular volumes in assessing cardiac function is that ventricular loading conditions strongly influence these variables. Thus, a depressed ejection fraction and lowered cardiac output may be observed in patients with normal ventricular function but with reduced preload, as occurs in hypovolemia, or with increased afterload, as occurs in acutely elevated arterial pressure. The end-systolic left ventricular pressure-volume relationship is a particularly useful index of ventricular performance since it does not depend on preload and afterload (Fig. 1-10). At any level of myocardial contractility, left ventricular end-systolic volume varies inversely with end-systolic pressure; as contractility declines, endsystolic volume (at any level of end-systolic pressure) rises.

CHAPTER 1

impulses to the heart, in heart rate, and in venous tone, will serve as compensatory mechanisms and sustain cardiac output in a normal individual.

SECTION I Introduction to Cardiovascular Disorders

Left ventricular pressure

16

Abnormal relaxation

Pericardial restraint

Increased chamber stiffness

Chamber dilation

Left ventricular volume

FIGURE 1-11 Mechanisms that cause diastolic dysfunction reflected in the pressure-volume relation. The bottom half of the pressure-volume loop is depicted. Solid lines represent normal subjects; broken lines represent patients with diastolic dysfunction. (From JD Carroll et al: The differential effects of positive inotropic and vasodilator therapy on diastolic properties in patients with congestive cardiomyopathy. Circulation 74:815, 1986; with permission.)

with hypertrophy and conditions that infiltrate the ventricle, such as amyloid, or by an extrinsic constraint (e.g., pericardial compression) (Fig. 1-11). Ventricular filling can be assessed by continuously measuring the velocity of flow across the mitral valve using Doppler ultrasound. Normally, the velocity of inflow is more rapid in early diastole than during atrial systole; with mild to moderately impaired relaxation, the rate of early diastolic filling declines, while the rate of presystolic filling rises. With further impairment of filling, the pattern is “pseudo-normalized,” and early ventricular filling becomes more rapid as left atrial pressure upstream to the stiff left ventricle rises.

CARDIAC METABOLISM The heart requires a continuous supply of energy (in the form of ATP) not only to perform its mechanical pumping functions but also to regulate intracellular and transsarcolemmal ionic movements and concentration gradients. Among its pumping functions, the development of tension, the frequency of contraction, and the level of myocardial contractility are the principal determinants of the heart’s substantial energy needs, making its O2 requirements approximately 15% of that of the entire organism.

Most ATP production depends on the oxidation of substrate [glucose and free fatty acids (FFAs)]. Myocardial FFAs are derived from circulating FFAs, which result principally from lipolysis of adipose tissue, while the myocyte’s glucose is obtained from plasma as well as from the cell’s breakdown of its glycogen stores (glycogenolysis). There is a reciprocal relation between the utilization of these two principal sources of acetyl CoA in cardiac muscle. Glucose is broken down in the cytoplasm into a three-carbon product, pyruvate, which passes into the mitochondria, where it is metabolized to the two-carbon fragment, acetyl coenzyme A, and undergoes oxidation. FFAs are converted to acyl-CoA in the cytoplasm and acetyl coenzyme A (Co-A) in the mitochondria. Acetyl Co-A enters the citric acid (Krebs) cycle to produce ATP by oxidative phosphorylation within the mitochondria; ATP then enters the cytoplasm from the mitochondrial compartment. Intracellular ADP, resulting from the breakdown of ATP, enhances mitochondrial ATP production. In the fasted, resting state, circulating FFA concentrations and their myocardial uptake are high, and they are the principal source of acetyl CoA (∼70%). In the fed state, with elevations of blood glucose and insulin, glucose oxidation increases and FFA oxidation subsides. Increased cardiac work, the administration of inotropic agents, hypoxia, and mild ischemia all enhance myocardial glucose uptake, glucose production resulting from glycogenolysis, and glucose metabolism to pyruvate (glycolysis). By contrast, β-adrenergic stimulation, as occurs during stress, raises the circulating levels and metabolism of FFAs in favor of glucose. Severe ischemia inhibits the cytoplasmic enzyme pyruvate dehydrogenase, and despite both glycogen and glucose breakdown, glucose is metabolized only to lactic acid (anaerobic glycolysis), which does not enter the citric acid cycle. Anaerobic glycolysis produces much less ATP than aerobic glucose metabolism, in which glucose is metabolized to pyruvate and subsequently oxidized to CO2. High concentrations of circulating FFAs, which can occur when adrenergic stimulation is superimposed on severe ischemia, reduce oxidative phosphorylation and also cause ATP wastage; the myocardial content of ATP declines, and myocardial contraction becomes impaired. In addition, products of FFA breakdown can exert toxic effects on cardiac cell membranes and may be arrhythmogenic. Myocardial energy is stored as creatine phosphate (CP), which is in equilibrium with ATP, the immediate source of energy. In states of reduced energy availability, the CP stores decline first. Cardiac hypertrophy, fibrosis, tachycardia, increased wall tension resulting from ventricular dilatation, and increased intracytoplasmic [Ca2+] all contribute to increased myocardial energy needs.When coupled with reduced coronary flow reserve, as occurs with obstruction of coronary arteries or abnormalities of the coronary microcirculation, an imbalance in myocardial ATP production relative to demand may occur, and the resulting ischemia can worsen or cause heart failure.

REGENERATING CARDIAC TISSUE

COLUCCI WS, BRAUNWALD E (eds): Atlas of Heart Failure: Cardiac Function and Dysfunction, 4th ed. Philadelphia, Current Medicine, 2004 DEANFIELD JE et al: Endothelial function and dysfunction: Testing and clinical relevance. Circulation 115:1285, 2007

Basic Biology of the Cardiovascular System

FURTHER READINGS

17

CHAPTER 1

Until very recently, the mammalian myocardium was viewed as an end-differentiated organ without regeneration potential. Resident and bone marrow–derived stem cells have now been identified, are currently being evaluated as sources of regenerative potential for the heart, and offer the exciting possibility of reconstructing an infarcted or failing ventricle.

KATZ AM: Physiology of the Heart, 4th ed. Philadelphia, Lippincott Williams and Wilkins, 2005 KIRBY ML: Cardiac Development, New York, Oxford University Press, 2007 LIBBY P et al: The vascular endothelium and atherosclerosis, in The Handbook of Experimental Pharmacology, S Moncada and EA Higgs (eds). Berlin-Heidelberg, Springer-Verlag, 2006 MAHONEY WM, SCHWARTZ SM: Defining smooth muscle cells and smooth muscle cell injury. J Clin Invest 15:221, 2005 OPIE LH: Heart Physiology: From Cell to Circulation, 4th ed. Philadelphia, Lippincott,Williams and Wilkins, 2004 ———: Mechanisms of cardiac contraction and relaxation, in Braunwald’s Heart Disease, 8th ed, P Libby et al (eds). Philadelphia, Elsevier, 2008 WEHRENS XH et al: Intracellular calcium release and cardiac disease. Annu Rev Physiol 67:69, 2005

CHAPTER 2

EPIDEMIOLOGY OF CARDIOVASCULAR DISEASE Thomas A. Gaziano

■

J. Michael Gaziano

■ The Epidemiologic Transition . . . . . . . . . . . . . . . . . . . . . . . . . . 18 The Epidemiologic Transition in the United States . . . . . . . . . . 19 Current Worldwide Variations . . . . . . . . . . . . . . . . . . . . . . . . . 20 ■ Global Trends in Cardiovascular Disease . . . . . . . . . . . . . . . . . 22 Regional Trends in Risk Factors . . . . . . . . . . . . . . . . . . . . . . . 23 Behavioral Risk Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Metabolic Risk Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

for , holosystolic, or late systolic

Other signs or symptoms of cardiac disease Echocardiography

Normal ECG and chest X-ray

No further workup

Abnormal ECG or chest X-ray

Cardiac consult if appropriate

FIGURE 3-1 An alternative “echocardiography first” approach to the evaluation of a heart murmur that also uses the results of the electrocardiogram (ECG) and chest x-ray in asymptomatic patients with soft midsystolic murmurs and no other physical findings. The algorithm is useful for patients older than 40 years in whom the prevalence of coronary artery disease and aortic stenosis increases as the cause of systolic murmur. [From RA O’Rourke, in Primary Cardiology, 2d ed, E Braunwald, L Goldman (eds). Philadelphia, Saunders, 2003.]

whose first clinical manifestation is syncope or even sudden death. However, the alert physician may recognize the patient at risk of these complications long before they occur and can often take measures to prevent their occurrence. For example, the patient with acute myocardial infarction will often have had risk factors for atherosclerosis for many years. Had these been recognized, their elimination or reduction might have delayed or even prevented the infarction. Similarly, the patient with hypertrophic cardiomyopathy may have had a heart murmur for years, and a family history of this disorder. These findings could have led to an echocardiographic examination and the recognition of the condition and appropriate therapy long before the occurrence of a serious acute manifestation. Patients with valvular heart disease or idiopathic dilated cardiomyopathy, on the other hand, may have a prolonged course of gradually increasing dyspnea and other manifestations of chronic heart failure that is punctuated by episodes of acute deterioration only late in the course of the disease. It is of great importance to understand the natural history of various cardiac disorders so as to apply diagnostic and therapeutic measures that are appropriate to each stage of the condition as well as to provide the patient and family with an estimate of the prognosis.

Increasing subspecialization in internal medicine and the perfection of advanced diagnostic techniques in cardiology can lead to several undesirable consequences. Examples include: 1. Failure by the noncardiologist to recognize important cardiac manifestations of systemic illnesses, e.g., the presence of mitral stenosis, patent foramen ovale, and/or transient atrial arrhythmia in a patient with stroke or the presence of pulmonary hypertension and cor pulmonale in a patient with scleroderma or Raynaud’s syndrome. A cardiovascular examination should be carried out to identify and estimate the severity of cardiovascular involvement that accompanies many noncardiac disorders. 2. Failure by the cardiologist to recognize underlying systemic disorders in patients with heart disease. For example, hyperthyroidism should be tested for in an elderly patient with atrial fibrillation and unexplained heart failure. Similarly, Lyme disease should be considered in a patient with unexplained fluctuating atrioventricular block. A cardiovascular abnormality may provide the clue critical to the recognition of some systemic disorders. For instance, an unexplained pericardial effusion may provide an early clue to the diagnosis of tuberculosis or neoplasm. 3. Overreliance on and overutilization of laboratory tests, particularly invasive techniques for the examination of the cardiovascular system. Cardiac catheterization and coronary arteriography (Chap. 13) provide precise diagnostic information that is critical to clinical evaluation which may be crucial in developing a therapeutic plan in patients with known or suspected CAD. Although a great deal of attention has been directed to these examinations, it is important to recognize that they serve to supplement, not supplant, a careful examination carried out by clinical and noninvasive techniques. A coronary arteriogram should not be carried out in lieu of a careful history in patients with chest pain suspected of having ischemic heart disease. Although coronary arteriography may establish whether the coronary arteries are obstructed, and if so the severity of the obstruction, the results of the procedure by themselves often do not provide a definite answer to the question of whether a patient’s complaint of chest discomfort is attributable to coronary arteriosclerosis and whether or not revascularization is indicated. Despite the value of invasive tests in certain circumstances, they entail some small risk to the patient, involve discomfort and substantial cost, and place a strain on medical facilities. Therefore, they should be carried

Approach to the Patient with Possible Cardiovascular Disease

Asymptomatic and no associated findings

Diastolic or Continuous Murmur

29

CHAPTER 3

Systolic Murmur

PITFALLS IN CARDIOVASCULAR MEDICINE

30 out only if, after the results of clinical examination and

SECTION I

assessment by noninvasive tests have been considered, the results (of the invasive examination) can be expected to modify the patient’s management.

DISEASE PREVENTION AND MANAGEMENT

Introduction to Cardiovascular Disorders

The prevention of heart disease, especially of CAD, is one of the most important tasks of primary care health givers as well as cardiologists. Prevention begins with risk assessment, followed by attention to lifestyle, such as achieving optimal weight and discontinuing smoking, and aggressive treatment of all abnormal risk factors, such as hypertension, hyperlipidemia, and diabetes mellitus. After a complete diagnosis has been established in patients with known heart disease, a number of management options are usually available. Several examples may be used to demonstrate some of the principles of cardiovascular therapeutics: 1. In the absence of evidence of heart disease, a clear, definitive statement to that effect should be made and the patient should not be asked to return at intervals for repeated examinations. If there is no evidence for disease, such continued attention may lead to the patient developing inappropriate anxiety and fixation on the heart. 2. If there is no evidence of cardiovascular disease but the patient has one or more risk factors for the development of ischemic heart disease (Chap. 33), a plan for risk reduction should be developed and the patient should be retested at intervals to assess compliance and that the risk factors are being reduced. 3. Asymptomatic or mildly symptomatic patients with valvular heart disease that is anatomically severe should be evaluated periodically, every 6 to 12 months, by clinical and noninvasive examinations. Early signs of deterioration of ventricular function may signify the need for surgical treatment before the development of disabling symptoms, irreversible myocardial damage, and excessive risk of surgical treatment (Chap. 20).

4. In patients with CAD (Chap. 33), available practice guidelines should be considered in the decision on the form of treatment (medical, percutaneous coronary intervention, or surgical revascularization). Mechanical revascularization, i.e., the latter two modalities, may be employed too frequently in the United States and perhaps too infrequently in Eastern Europe and developing nations. The mere presence of angina pectoris and/or the demonstration of critical coronary arterial narrowing at angiography should not reflexly evoke a decision to treat the patient by revascularization. Instead, these procedures should be limited to patients with CAD whose angina has not responded adequately to medical treatment or in whom revascularization has been shown to improve the natural history (e.g., acute coronary syndrome, or multivessel CAD with left ventricular dysfunction). FURTHER READINGS ABRAMS J: Synopsis of Cardiac Physical Diagnosis, 2d ed. Oxford, Butterworth Heinemann, 2001 AMERICAN HEART ASSOCIATION: Heart Disease and Stroke Statistics, 2006 Update. Dallas, TX, American Heart Association, www. americanheart.org AMERICAN HEART ASSOCIATION: Heart Disease and Stroke Statistics, 2009 Update. Dallas, TX, American Heart Association, www. americanheart.org MORROW DA et al: Chronic coronary artery disease, in Braunwald’s Heart Disease, 8th ed, P Libby et al (eds). Philadelphia, Saunders, 2008 NATIONAL HEART, LUNG AND BLOOD INSTITUTE: FY 2005 Fact Book. Bethesda, MD, National Heart, Lung and Blood Institute, 2006 THE CRITERIA COMMITTEE OF THE NEW YORK HEART ASSOCIATION: Nomenclature and Criteria for Diagnosis, 9th ed. Boston, Little, Brown, 1994 THE NHLBI-SPONSORED WOMEN’S ISCHEMIA SYNDROME EVALUATION (WISE): Challenging existing paradigms in ischemic heart disease. J Am Coll Cardiol 47(Suppl S):1, 2006 VANDEN BELT J: The history, in Classic Teachings in Clinical Cardiology: A Tribute to W. Proctor Harvey, M Chizner (ed). Cedar Grove, NJ, Laennec, 1996, pp 41–54

SECTION II

DIAGNOSIS OF CARDIOVASCULAR DISORDERS

CHAPTER 4

CHEST DISCOMFORT Thomas H. Lee

Causes of Chest Discomfort . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Guidelines and Critical Pathways for Acute Chest Discomfort . . 38 Nonacute Chest Discomfort . . . . . . . . . . . . . . . . . . . . . . . . . . 39 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

Chest discomfort is one of the most common challenges for clinicians in the office or emergency department.The differential diagnosis includes conditions affecting organs throughout the thorax and abdomen, with prognostic implications that range from benign to life-threatening (Table 4-1). Failure to recognize potentially serious conditions such as acute ischemic heart disease, aortic dissection, tension pneumothorax, or pulmonary embolism can lead to serious complications, including death. Conversely, overly conservative management of low-risk patients leads to unnecessary hospital admissions, tests, procedures, and anxiety.

Angina Pectoris

(See also Chap. 33) The chest discomfort of myocardial ischemia is a visceral discomfort that is usually described as a heaviness, pressure, or squeezing (Table 4-2). Other common adjectives for anginal pain are burning and aching. Some patients deny any “pain” but may admit to dyspnea or a vague sense of anxiety.The word “sharp” is sometimes used by patients to describe intensity rather than quality. The location of angina pectoris is usually retrosternal; most patients do not localize the pain to any small area. The discomfort may radiate to the neck, jaw, teeth, arms, or shoulders, reflecting the common origin in the posterior horn of the spinal cord of sensory neurons supplying the heart and these areas. Some patients present with aching in sites of radiated pain as their only symptoms of ischemia. Occasional patients report epigastric distress with ischemic episodes. Less common is radiation to below the umbilicus or to the back. Stable angina pectoris usually develops gradually with exertion, emotional excitement, or after heavy meals. Rest or treatment with sublingual nitroglycerin typically leads to relief within several minutes. In contrast, pain that is fleeting (lasting only a few seconds) is rarely ischemic in origin. Similarly, pain that lasts for several hours is unlikely to represent angina, particularly if the patient’s electrocardiogram (ECG) does not show evidence of ischemia. Anginal episodes can be precipitated by any physiologic or psychological stress that induces tachycardia. Most myocardial perfusion occurs during diastole, when there is minimal pressure opposing coronary artery flow

CAUSES OF CHEST DISCOMFORT Myocardial Ischemia and Injury Myocardial ischemia occurs when the oxygen supply to the heart is not sufficient to meet metabolic needs. This mismatch can result from a decrease in oxygen supply, a rise in demand, or both. The most common underlying cause of myocardial ischemia is obstruction of coronary arteries by atherosclerosis; in the presence of such obstruction, transient ischemic episodes are usually precipitated by an increase in oxygen demand as a result of physical exertion. However, ischemia can also result from psychological stress, fever, or large meals or from compromised oxygen delivery due to anemia, hypoxia, or hypotension. Ventricular hypertrophy due to valvular heart disease, hypertrophic cardiomyopathy, or hypertension can predispose the myocardium to ischemia because of impaired penetration of blood flow from epicardial coronary arteries to the endocardium.

32

TABLE 4-1 DIFFERENTIAL DIAGNOSES OF PATIENTS ADMITTED TO HOSPITAL WITH ACUTE CHEST DISCOMFORT RULED NOT MYOCARDIAL INFARCTION DIAGNOSIS

PERCENT

42

a

In order of frequency. Source: P Fruergaard et al: Eur Heart J 17:1028, 1996.

from within the left ventricle. Since tachycardia decreases the percentage of the time in which the heart is in diastole, it decreases myocardial perfusion. Unstable Angina and Myocardial Infarction

(See also Chaps. 34 and 35) Patients with these acute ischemic syndromes usually complain of symptoms similar in quality to angina pectoris, but more prolonged and severe.The onset of these syndromes may occur with the patient at rest, or awakened from sleep, and sublingual nitroglycerin may lead to transient or no relief. Accompanying symptoms may include diaphoresis, dyspnea, nausea, and light-headedness. The physical examination may be completely normal in patients with chest discomfort due to ischemic heart disease. Careful auscultation during ischemic episodes may reveal a third or fourth heart sound, reflecting myocardial systolic or diastolic dysfunction. A transient murmur of mitral regurgitation suggests ischemic papillary muscle dysfunction. Severe episodes of ischemia can lead to pulmonary congestion and even pulmonary edema. Other Cardiac Causes

Myocardial ischemia caused by hypertrophic cardiomyopathy or aortic stenosis leads to angina pectoris similar to that caused by coronary atherosclerosis. In such cases, a loud systolic murmur or other findings usually suggest that abnormalities other than coronary atherosclerosis may be contributing to the patient’s symptoms. Some patients with chest pain and normal coronary angiograms have functional abnormalities of the coronary circulation, ranging from coronary spasm visible on coronary angiography to abnormal vasodilator responses and

Pericarditis (See also Chap. 22) The pain in pericarditis is believed to be due to inflammation of the adjacent parietal pleura, since most of the pericardium is believed to be insensitive to pain. Thus, infectious pericarditis, which usually involves adjoining pleural surfaces, tends to be associated with pain, while conditions that cause only local inflammation (e.g., myocardial infarction or uremia) and cardiac tamponade tend to result in mild or no chest pain. The adjacent parietal pleura receives its sensory supply from several sources, so the pain of pericarditis can be experienced in areas ranging from the shoulder and neck to the abdomen and back. Most typically, the pain is retrosternal and is aggravated by coughing, deep breaths, or changes in position—all of which lead to movements of pleural surfaces. The pain is often worse in the supine position and relieved by sitting upright and leaning forward. Less common is a steady aching discomfort that mimics acute myocardial infarction. Diseases of the Aorta (See also Chap. 38) Aortic dissection is a potentially catastrophic condition that is due to spread of a subintimal hematoma within the wall of the aorta. The hematoma may begin with a tear in the intima of the aorta or with rupture of the vasa vasorum within the aortic media. This syndrome can occur with trauma to the aorta, including motor vehicle accidents or medical procedures in which catheters or intraaortic balloon pumps damage the intima of the aorta. Nontraumatic aortic dissections are rare in the absence of hypertension and/or conditions associated with deterioration of the elastic or muscular components of the media within the aorta’s wall. Cystic medial degeneration is a feature of several inherited connective tissue diseases, including Marfan and EhlersDanlos syndromes. About half of all aortic dissections in women younger than 40 years occur during pregnancy. Almost all patients with acute dissections present with severe chest pain, although some patients with chronic dissections are identified without associated symptoms. Unlike the pain of ischemic heart disease, symptoms of aortic dissection tend to reach peak severity immediately, often causing the patient to collapse from its intensity. The classic teaching is that the adjectives used to

Chest Discomfort

31 28 4 2 2 1.5 1 1 1

CHAPTER 4

Gastroesophageal diseasea Gastroesophageal reflux Esophageal motility disorders Peptic ulcer Gallstones Ischemic heart disease Chest wall syndromes Pericarditis Pleuritis/pneumonia Pulmonary embolism Lung cancer Aortic aneurysm Aortic stenosis Herpes zoster

heightened vasoconstrictor responses. The term “cardiac 33 syndrome X” is used to describe patients with angina-like chest pain and ischemic-appearing ST-segment depression during stress despite normal coronary arteriograms. Some data indicate that many such patients have limited changes in coronary flow in response to pacing stress or coronary vasodilators. Despite the possibility that chest pain may be due to myocardial ischemia in such patients, their prognosis is excellent.

34

TABLE 4-2 TYPICAL CLINICAL FEATURES OF MAJOR CAUSES OF ACUTE CHEST DISCOMFORT

SECTION II Diagnosis of Cardiovascular Disorders

CONDITION

DURATION

QUALITY

LOCATION

ASSOCIATED FEATURES

Angina

More than 2 and less than 10 min

Pressure, tightness, squeezing, heaviness, burning

Unstable angina

10–20 min

Similar to angina but often more severe

Retrosternal, often with radiation to or isolated discomfort in neck, jaw, shoulders, or arms— frequently on left Similar to angina

Acute myocardial infarction

Variable; often more than 30 min

Similar to angina but often more severe

Similar to angina

Aortic stenosis

Recurrent episodes as described for angina Hours to days; may be episodic

As described for angina

As described for angina

Sharp

Aortic dissection

Abrupt onset of unrelenting pain

Tearing or ripping sensation; knifelike

Retrosternal or toward cardiac apex; may radiate to left shoulder Anterior chest, often radiating to back, between shoulder blades

Pulmonary embolism

Abrupt onset; several minutes to a few hours Variable

Pleuritic

Often lateral, on the side of the embolism

Pressure

Substernal

Variable

Pleuritic

Sudden onset; several hours

Pleuritic

Unilateral, often localized Lateral to side of pneumothorax

Esophageal reflux

10–60 min

Burning

Substernal, epigastric

Esophageal spasm Peptic ulcer Gallbladder disease Musculoskeletal disease

2–30 min

Retrosternal

Prolonged Prolonged

Pressure, tightness, burning Burning Burning, pressure

Precipitated by exertion, exposure to cold, psychologic stress S4 gallop or mitral regurgitation murmur during pain Similar to angina, but occurs with low levels of exertion or even at rest Unrelieved by nitroglycerin May be associated with evidence of heart failure or arrhythmia Late-peaking systolic murmur radiating to carotid arteries May be relieved by sitting up and leaning forward Pericardial friction rub Associated with hypertension and/or underlying connective tissue disorder, e.g., Marfan syndrome Murmur of aortic insufficiency, pericardial rub, pericardial tamponade, or loss of peripheral pulses Dyspnea, tachypnea, tachycardia, and hypotension Dyspnea, signs of increased venous pressure including edema and jugular venous distention Dyspnea, cough, fever, rales, occasional rub Dyspnea, decreased breath sounds on side of pneumothorax Worsened by postprandial recumbency Relieved by antacids Can closely mimic angina

Variable

Aching

Epigastric, substernal Epigastric, right upper quadrant, substernal Variable

Herpes zoster

Variable

Sharp or burning

Dermatomal distribution

Emotional and psychiatric conditions

Variable; may be fleeting

Variable

Variable; may be retrosternal

Pericarditis

Pulmonary hypertension

Pneumonia or pleuritis Spontaneous pneumothorax

Relieved with food or antacids May follow meal Aggravated by movement May be reproduced by localized pressure on examination Vesicular rash in area of discomfort Situational factors may precipitate symptoms Anxiety or depression often detectable with careful history

from myocardial syndromes. Acid reflux typically causes 35 a deep burning discomfort that may be exacerbated by alcohol, aspirin, or some foods; the discomfort is often relieved by antacid or other acid-reducing therapies. Acid reflux tends to be exacerbated by lying down and may be worse in early morning when the stomach is empty of food that might otherwise absorb gastric acid. Esophageal spasm may occur in the presence or absence of acid reflux and leads to a squeezing pain indistinguishable from angina. Prompt relief of esophageal spasm is often provided by antianginal therapies such as sublingual nifedipine, further promoting confusion between these syndromes. Chest pain can also result from injury to the esophagus, such as a Mallory-Weiss tear caused by severe vomiting. Chest pain can result from diseases of the gastrointestinal tract below the diaphragm, including peptic ulcer disease, biliary disease, and pancreatitis. These conditions usually cause abdominal pain as well as chest discomfort; symptoms are not likely to be associated with exertion. The pain of ulcer disease typically occurs 60 to 90 min after meals, when postprandial acid production is no longer neutralized by food in the stomach. Cholecystitis usually causes a pain that is described as aching, occurring an hour or more after meals.

CHAPTER 4 Chest Discomfort

describe the pain reflect the process occurring within the wall of the aorta—“ripping” and “tearing”—but more recent data suggest that the most common presenting complaint is sudden onset of severe, sharp pain.The location often correlates with the site and extent of the dissection. Thus, dissections that begin in the ascending aorta and extend to the descending aorta tend to cause pain in the front of the chest that extends into the back, between the shoulder blades. Physical findings may also reflect extension of the aortic dissection that compromises flow into arteries branching off the aorta. Thus, loss of a pulse in one or both arms, cerebrovascular accident, or paraplegia can all be catastrophic consequences of aortic dissection. Hematomas that extend proximally and undermine the coronary arteries or aortic valve apparatus may lead to acute myocardial infarction or acute aortic insufficiency. Rupture of the hematoma into the pericardial space leads to pericardial tamponade. Another abnormality of the aorta that can cause chest pain is a thoracic aortic aneurysm. Aortic aneurysms are frequently asymptomatic but can cause chest pain and other symptoms by compressing adjacent structures.This pain tends to be steady, deep, and sometimes severe. Pulmonary Embolism Chest pain caused by pulmonary embolism is believed to be due to distention of the pulmonary artery or infarction of a segment of the lung adjacent to the pleura. Massive pulmonary emboli may lead to substernal pain that is suggestive of acute myocardial infarction. More commonly, smaller emboli lead to focal pulmonary infarctions that cause pain that is lateral and pleuritic.Associated symptoms include dyspnea and, occasionally, hemoptysis. Tachycardia is usually present. Although not always present, certain characteristic ECG changes can support the diagnosis. Pneumothorax Sudden onset of pleuritic chest pain and respiratory distress should lead to consideration of spontaneous pneumothorax, as well as pulmonary embolism. Such events may occur without a precipitating event in persons without lung disease, or as a consequence of underlying lung disorders.

Neuromusculoskeletal Conditions Cervical disk disease can cause chest pain by compression of nerve roots. Pain in a dermatomal distribution can also be caused by intercostal muscle cramps or by herpes zoster. Chest pain symptoms due to herpes zoster may occur before skin lesions are apparent. Costochondral and chondrosternal syndromes are the most common causes of anterior chest musculoskeletal pain. Only occasionally are physical signs of costochondritis such as swelling, redness, and warmth (Tietze’s syndrome) present. The pain of such syndromes is usually fleeting and sharp, but some patients experience a dull ache that lasts for hours. Direct pressure on the chondrosternal and costochondral junctions may reproduce the pain from these and other musculoskeletal syndromes. Arthritis of the shoulder and spine and bursitis may also cause chest pain. Some patients who have these conditions and myocardial ischemia blur and confuse symptoms of these syndromes.

Pneumonia or Pleuritis Lung diseases that damage and cause inflammation of the pleura of the lung usually cause a sharp, knifelike pain that is aggravated by inspiration or coughing. Gastrointestinal Conditions Esophageal pain from acid reflux from the stomach, spasm, obstruction, or injury can be difficult to discern

Emotional and Psychiatric Conditions As great as 10% of patients who present to emergency departments with acute chest discomfort have panic disorder or other emotional conditions.The symptoms in these populations are highly variable, but frequently the discomfort is described as visceral tightness or aching that lasts more than 30 min. Some patients offer other atypical descriptions, such as pain that is fleeting, sharp,

36 and/or localized to a small region. The ECG in patients with emotional conditions may be difficult to interpret if hyperventilation causes ST-T-wave abnormalities. A careful history may elicit clues of depression, prior panic attacks, somatization, agoraphobia, or other phobias.

SECTION II

Approach to the Patient: CHEST DISCOMFORT

Diagnosis of Cardiovascular Disorders

The evaluation of the patient with chest discomfort must accommodate two goals—determining the diagnosis and assessing the safety of the immediate management plan. The latter issue is often dominant when the patient has acute chest discomfort, such as patients seen in the emergency department. In such settings, the clinician must focus first on identifying patients who require aggressive interventions to diagnose or manage potentially life-threatening conditions, including acute ischemic heart disease, acute aortic dissection, pulmonary embolism, and tension pneumothorax. If such conditions are unlikely, the clinician must address questions such as the safety of discharge to home, admission to a non-coronary care unit facility, or immediate exercise testing. Table 4-3 displays a sequence of questions that can be used in the evaluation of the patient with chest discomfort, with the diagnostic entities that are most important for consideration at each stage of the evaluation.

ACUTE CHEST DISCOMFORT In patients with acute chest discomfort, the clinician must first assess the patient’s respiratory and hemodynamic status. If either is compromised, initial management should focus on stabilizing the patient before the diagnostic evaluation is pursued. If, however, the patient does not require emergent interventions, a focused history, physical examination, and laboratory evaluation should then be performed to assess the patient’s risk of life-threatening conditions. Clinicians who are seeing patients in the office setting should not assume that they do not have acute ischemic heart disease, even if the prevalence may be lower. Malpractice litigation related to myocardial infarctions that were missed during office evaluations is becoming increasingly common, and ECGs were not performed in many such cases. The prevalence of high-risk patients seen in office settings may be increasing due to congestion in emergency departments. In either setting, the history should include questions about the quality and location of the chest discomfort (Table 4-2). The patient should also be asked about the nature of onset of the pain and its duration. Myocardial ischemia is usually associated with a gradual intensification of symptoms over a period of minutes. Pain that is fleeting or that lasts hours without being associated with electrocardiographic changes is not likely to be ischemic in origin. Although the presence of risk factors for coronary artery disease may heighten concern for this diagnosis,

TABLE 4-3 CONSIDERATIONS IN THE ASSESSMENT OF THE PATIENT WITH CHEST DISCOMFORT 1. Could the chest discomfort be due to an acute, potentially life-threatening condition that warrants immediate hospitalization and aggressive evaluation? Acute ischemic heart disease Pulmonary embolism Aortic dissection Spontaneous pneumothorax 2. If not, could the discomfort be due to a chronic condition likely to lead to serious complications? Stable angina Aortic stenosis Pulmonary hypertension 3. If not, could the discomfort be due to an acute condition that warrants specific treatment? Pericarditis Pneumonia/pleuritis Herpes zoster 4. If not, could the discomfort be due to another treatable chronic condition? Esophageal reflux Cervical disk disease Esophageal spasm Arthritis of the shoulder or spine Peptic ulcer disease Costochondritis Gallbladder disease Other musculoskeletal disorders Other gastrointestinal conditions Anxiety state

37

INCREASED LIKELIHOOD OF AMI Radiation to right arm or shoulder Radiation to both arms or shoulders Associated with exertion Radiation to left arm Associated with diaphoresis Associated with nausea or vomiting Worse than previous angina or similar to previous MI

CHAPTER 4

Described as pressure DECREASED LIKELIHOOD OF AMI Inframammary location Reproducible with palpation Described as sharp Described as positional

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Likelihood ratio for AMI

FIGURE 4-1 Impact of chest pain characteristics on odds of acute myocardial infarction (AMI). (Figure prepared from data in Swap and Nagurney.)

the absence of such risk factors does not lower the risk for myocardial ischemia enough to be used to justify a decision to discharge a patient. Wide radiation of chest pain increases probability that pain is due to myocardial infarction. Radiation of chest pain to the left arm is common with acute ischemic heart disease, but radiation to the right arm is also highly consistent with this diagnosis. Figure 4-1 shows estimates derived from several studies of the impact of various clinical features from the history on the probability that a patient has an acute myocardial infarction. Right shoulder pain is also common with acute cholecystitis, but this syndrome is usually accompanied by pain that is located in the abdomen rather than chest. Chest pain that radiates between the scapulae raises the question of aortic dissection. The physical examination should include evaluation of blood pressure in both arms and of pulses in both legs. Poor perfusion of a limb may be due to an aortic dissection that has compromised flow to an artery branching from the aorta. Chest auscultation may reveal diminished breath sounds; a pleural rub; or evidence of pneumothorax, pulmonary embolism, pneumonia, or pleurisy. Tension pneumothorax may lead to a shift in the trachea from the midline, away from the side of the pneumothorax. The cardiac examination should seek pericardial rubs, systolic and diastolic murmurs, and third or fourth heart sounds. Pressure on the chest wall may reproduce symptoms

in patients with musculoskeletal causes of chest pain; it is important that the clinician ask the patient if the chest pain syndrome is being completely reproduced before drawing too much reassurance that more serious underlying conditions are not present. An ECG is an essential test for adults with chest discomfort that is not due to an obvious traumatic cause. In such patients, the presence of electrocardiographic changes consistent with ischemia or infarction (Chap. 11) is associated with high risks of acute myocardial infarction or unstable angina (Table 4-4); such patients should be admitted to a unit with electrocardiographic monitoring and the capacity to respond to a cardiac arrest. The absence of such changes does not exclude acute ischemic heart disease, but the risk of life-threatening complications is low for patients with normal electrocardiograms or only nonspecific ST-T-wave changes. If these patients are not considered appropriate for immediate discharge, they are often candidates for early or immediate exercise testing. Markers of myocardial injury are often obtained in the emergency department evaluation of acute chest discomfort.The most commonly used markers are creatine kinase (CK), CK-MB, and the cardiac troponins (I and T). Rapid bedside assays of the cardiac troponins have been developed and shown to be sufficiently accurate to predict prognosis and guide management. Some data support the use of other markers, such as serum myoglobin, C-reactive protein (CRP), placental

Chest Discomfort

Described as pleuritic

38

TABLE 4-4 PREVALENCE OF MYOCARDIAL INFARCTION AND UNSTABLE ANGINA AMONG SUBSETS OF PATIENTS WITH ACUTE CHEST DISCOMFORT IN THE EMERGENCY DEPARTMENT PREVALENCE

FINDING

SECTION II Diagnosis of Cardiovascular Disorders

ST elevation (≥1 mm) or Q waves on ECG not known to be old Ischemia or strain on ECG not known to be old (ST depression ≥1 mm or ischemic T waves) None of the preceding ECG changes but a prior history of angina or myocardial infarction (history of heart attack or nitroglycerin use) None of the preceding ECG changes and no prior history of angina or myocardial infarction (history of heart attack or nitroglycerin use)

MYOCARDIAL INFARCTION, %

UNSTABLE ANGINA, %

79

12

20

41

4

51

2

14

Note: ECG, electrocardiogram. Source: Unpublished data from Brigham and Women’s Hospital Chest Pain Study, 1997–1999.

growth factor, myeloperoxidase, and B-type natriuretic peptide (BNP); their roles are the subject of ongoing research. Single values of any of these markers do not have high sensitivity for acute myocardial infarction or for prediction of complications. Hence, decisions to discharge patients home should not be made on the basis of single negative values of these tests. Provocative tests for coronary artery disease are not appropriate for patients with ongoing chest pain. In such patients, rest myocardial perfusion scans can be considered; a normal scan reduces the likelihood of coronary artery disease and can help avoid admission of low-risk patients to the hospital. Promising early results suggest that 64-slice computed tomography (CT) and cardiac magnetic resonance imaging (MRI) may be of sufficient accuracy for diagnosis of coronary disease that these technologies may become widely used for patients with acute chest pain in whom the diagnosis is not clear. Clinicians frequently employ therapeutic trials with sublingual nitroglycerin or antacids or, in the stable

patient seen in the office setting, a proton pump inhibitor. A common error is to assume that a response to any of these interventions clarifies the diagnosis. While such information is often helpful, the patient’s response may be due to the placebo effect. Hence, myocardial ischemia should never be considered excluded solely because of a response to antacid therapy. Similarly, failure of nitroglycerin to relieve pain does not exclude the diagnosis of coronary disease. If the patient’s history or examination is consistent with aortic dissection, imaging studies to evaluate the aorta must be pursued promptly because of the high risk of catastrophic complications with this condition. Appropriate tests include a chest CT scan with contrast, MRI, or transesophageal echocardiography (TEE). Acute pulmonary embolism should be considered in patients with respiratory symptoms, pleuritic chest pain, hemoptysis, or a history of venous thromboembolism or coagulation abnormalities. Initial tests usually include CT angiography or a lung scan, which are sometimes combined with lower extremity venous ultrasound or D-dimer testing. If patients with acute chest discomfort show no evidence of life-threatening conditions, the clinician should then focus on serious chronic conditions with the potential to cause major complications, the most common of which is stable angina. Early use of exercise electrocardiography, stress echocardiography, or stress perfusion imaging for such patients, whether in the office or the emergency department, is now an accepted management strategy for low-risk patients. Exercise testing is not appropriate, however, for patients who (1) report pain that is believed to be ischemic occurring at rest or (2) have electrocardiographic changes not known to be old that are consistent with ischemia. Patients with sustained chest discomfort who do not have evidence for life-threatening conditions should be evaluated for evidence of conditions likely to benefit from acute treatment (Table 4-3). Pericarditis may be suggested by the history, physical examination, and ECG (Table 4-2). Clinicians should carefully assess blood pressure patterns and consider echocardiography in such patients to detect evidence of impending pericardial tamponade. Chest x-rays can be used to evaluate the possibility of pulmonary disease.

GUIDELINES AND CRITICAL PATHWAYS FOR ACUTE CHEST DISCOMFORT Guidelines for the initial evaluation for patients with acute chest pain have been developed by the American College

emergent reperfusion therapy, either via percutaneous coronary interventions or thrombolytic agents, is likely to lead to improved outcomes. • Triage to non-coronary care unit monitored facilities such as intermediate-care units or chest pain units of patients with a low risk for complications, such as patients without new ischemic changes on their ECGs and without ongoing chest pain. Such patients can usually be safely observed in non-coronary care unit settings, undergo early exercise testing, or be discharged home. Risk stratification can be assisted through use of prospectively validated multivariate algorithms that have been published for acute ischemic heart disease and its complications. • Shortening lengths of stay in the coronary care unit and hospital. Recommendations regarding the minimum length of stay in a monitored bed for a patient who has no further symptoms have decreased in recent years to 12 h or less if exercise testing or other risk stratification technologies are available.

NONACUTE CHEST DISCOMFORT The management of patients who do not require admission to the hospital or who no longer require inpatient observation includes identification of the cause of

FURTHER READINGS BRENNAN ML et al: Prognostic value of myeloperoxidase in patients with chest pain. N Engl J Med 349:1595, 2003 GIBBONS RJ et al: ACC/AHA 2002 guideline update for exercise testing. A report of the American College of Cardiology/ American Heart Association Task Force on Practice Guidelines (Committee on Exercise Testing). Available at www.acc.org/ qualityandscience/clinical/guidelines/exercise/dirindex.htm. Accessed on January 22, 2006 GIBSON PB et al: Low event rate for stress-only perfusion imaging in patients evaluated for chest pain. J Am Coll Cardiol 39:999, 2002 HEESCHEM C et al: Prognostic value of placental growth factor in patients with chest pain. JAMA 291:435, 2004 KWONG RY et al: Detecting acute coronary syndrome in the emergency department with cardiac magnetic resonance imaging. Circulation 197:531, 2003 LEBER AW et al: Quantification of obstructive and nonobstructive coronary lesions of 64-slice computed tomography. J Am Coll Cardiol 46:147, 2005 MILLER JM et al: Diagnostic performance of coronary angiography by 64-row CT. N Engl J Med 359:2324, 2008 SAENGER AK, JAFFE AS: Requiem for a heavyweight: the demise of ceratin kinase-MB. Circulation 118:2200, 2008 SEQUIST T, LEE TH: Prediction of missed myocardial infarction among symptomatic outpatients without coronary heart disease. Am Heart J 149:74, 2005 SEQUIST TD et al: Missed opportunities in the primary care management of early acute ischemic heart disease. Arch Intern Med 166: 2237, 2006 SUZUKI T et al: Diagnosis of acute aortic dissection by D-dimer. Circulation 119:2702, 2009 SWAP CJ, NAGURNEY JT:Value and limitations of chest pain history in the evaluation of patients with suspected acute coronary syndromes. JAMA 294:2623, 2005 TONG KL et al: Myocardial contrast echocardiography versus Thrombolysis in Myocardial Infarction score in patients presenting to the emergency department with chest pain and a nondiagnostic electrocardiogram. J Am Coll Cardiol 46:928, 2005 TSAI TT et al:Acute aortic syndromes. Circulation 205:3802, 2005

Chest Discomfort

• Rapid identification and treatment of patients for whom

the symptoms and the likelihood of major complica- 39 tions. Noninvasive tests for coronary disease serve to diagnose the condition and to identify patients with highrisk forms of coronary disease who may benefit from revascularization. Gastrointestinal causes of chest pain can be evaluated via endoscopy or radiology studies, or with trials of medical therapy. Emotional and psychiatric conditions warrant appropriate evaluation and treatment; randomized trial data indicate that cognitive therapy and group interventions lead to decreases in symptoms for such patients.

CHAPTER 4

of Cardiology, American Heart Association, and other organizations.These guidelines recommend performance of an ECG for all patients with chest pain who do not have an obvious noncardiac cause of their pain, and performance of a chest x-ray for patients with signs or symptoms consistent with congestive heart failure, valvular heart disease, pericardial disease, or aortic dissection or aneurysm. The American College of Cardiology/American Heart Association guidelines on exercise testing support its use in low-risk patients presenting to the emergency department, as well as in selected intermediate-risk patients. However, these guidelines emphasize that exercise tests should be performed only after patients have been screened for high-risk features or other indicators for hospital admission. Many medical centers have adopted critical pathways and other forms of guidelines to increase efficiency and to expedite the treatment of patients with high-risk acute ischemic heart disease syndromes.These guidelines emphasize the following strategies:

CHAPTER 5

DYSPNEA AND PULMONARY EDEMA Richard M. Schwartzstein

■ Dyspnea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Mechanisms of Dyspnea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 Assessing Dyspnea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 Differential Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 ■ Pulmonary Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44 Mechanisms of Fluid Accumulation . . . . . . . . . . . . . . . . . . . . . 44 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46

the system are normal.The increased neural output from the motor cortex is thought to be sensed due to a corollary discharge that is sent to the sensory cortex at the same time that signals are sent to the ventilatory muscles.

DYSPNEA The American Thoracic Society defines dyspnea as a “subjective experience of breathing discomfort that consists of qualitatively distinct sensations that vary in intensity. The experience derives from interactions among multiple physiological, psychological, social, and environmental factors, and may induce secondary physiological and behavioral responses.” Dyspnea, a symptom, must be distinguished from the signs of increased work of breathing.

Sensory Afferents Chemoreceptors in the carotid bodies and medulla are activated by hypoxemia, acute hypercapnia, and acidemia. Stimulation of these receptors, as well as others that lead to an increase in ventilation, produce a sensation of air hunger. Mechanoreceptors in the lungs, when stimulated by bronchospasm, lead to a sensation of chest tightness. J receptors, sensitive to interstitial edema, and pulmonary vascular receptors, activated by acute changes in pulmonary artery pressure, appear to contribute to air hunger. Hyperinflation is associated with the sensation of an inability to get a deep breath or of an unsatisfying breath. It is not clear if this sensation arises from receptors in the lungs or chest wall, or if it is a variant of the sensation of air hunger. Metaboreceptors, located in skeletal muscle, are believed to be activated by changes in the local biochemical milieu of the tissue active during exercise and, when stimulated, contribute to the breathing discomfort.

MECHANISMS OF DYSPNEA Respiratory sensations are the consequence of interactions between the efferent, or outgoing, motor output from the brain to the ventilatory muscles (feed-forward) and the afferent, or incoming, sensory input from receptors throughout the body (feedback), as well as the integrative processing of this information that we infer must be occurring in the brain (Fig. 5-1).A given disease state may lead to dyspnea by one or more mechanisms, some of which may be operative under some circumstances but not others. Motor Efferents Disorders of the ventilatory pump are associated with increased work of breathing or a sense of an increased effort to breathe.When the muscles are weak or fatigued, greater effort is required, even though the mechanics of

Integration: Efferent-Reafferent Mismatch A discrepancy or mismatch between the feed-forward message to the ventilatory muscles and the feedback

40

ALGORITHM FOR THE INPUTS IN DYSPNEA PRODUCTION

Sensory cortex Feedback

Mechanoreceptors Metaboreceptors

Feedforward

Corollary discharge Motor cortex

Error Signal Ventilatory muscles

from receptors that monitor the response of the ventilatory pump increases the intensity of dyspnea. This is particularly important when there is a mechanical derangement of the ventilatory pump, such as in asthma or chronic obstructive pulmonary disease (COPD). Anxiety Acute anxiety may increase the severity of dyspnea either by altering the interpretation of sensory data or by leading to patterns of breathing that heighten physiologic abnormalities in the respiratory system. In patients with expiratory flow limitation, for example, the increased respiratory rate that accompanies acute anxiety leads to hyperinflation, increased work of breathing, a sense of an increased effort to breathe, and a sense of an unsatisfying breath.

ASSESSING DYSPNEA Quality of Sensation As with pain, dyspnea assessment begins with a determination of the quality of the discomfort (Table 5-1). Dyspnea questionnaires, or lists of phrases commonly used by patients, assist those who have difficulty describing their breathing sensations.

PATHOPHYSIOLOGY

Chest tightness or constriction

Bronchoconstriction, interstitial edema (asthma, myocardial ischemia) Airway obstruction, neuromuscular disease (COPD, moderate to severe asthma, myopathy, kyphoscoliosis) Increased drive to breathe (CHF, pulmonary embolism, moderate to severe airflow obstruction) Hyperinflation (asthma, COPD) and restricted tidal volume (pulmonary fibrosis, chest wall restriction) Deconditioning

Increased work or effort of breathing

Air hunger, need to breathe, urge to breathe

Cannot get a deep breath, unsatisfying breath

Heavy breathing, rapid breathing, breathing more

Note: CHF, congestive heart failure; COPD, chronic obstructive pulmonary disease. Source: From Schwartzstein and Feller-Kopman.

Sensory Intensity A modified Borg scale or visual analogue scale can be utilized to measure dyspnea at rest, immediately following exercise, or on recall of a reproducible physical task, e.g., climbing the stairs at home. An alternative approach is to inquire about the activities a patient can do, i.e., to gain a sense of the patient’s disability. The Baseline Dyspnea Index and the Chronic Respiratory Disease Questionnaire are tools commonly used for this purpose. Affective Dimension For a sensation to be reported as a symptom, it must be perceived as unpleasant and interpreted as abnormal.We are still in the early stages of learning the best ways to assess the affective dimension of dyspnea. Some therapies for dyspnea, such as pulmonary rehabilitation, may reduce breathing discomfort, in part, by altering this dimension.

DIFFERENTIAL DIAGNOSIS Dyspnea is the consequence of deviations from normal function in the cardiopulmonary systems.Alterations in the

Dyspnea and Pulmonary Edema

FIGURE 5-1 Hypothetical model for integration of sensory inputs in the production of dyspnea. Afferent information from the receptors throughout the respiratory system projects directly to the sensory cortex to contribute to primary qualitative sensory experiences and provide feedback on the action of the ventilatory pump. Afferents also project to the areas of the brain responsible for control of ventilation. The motor cortex, responding to input from the control centers, sends neural messages to the ventilatory muscles and a corollary discharge to the sensory cortex (feed-forward with respect to the instructions sent to the muscles). If the feed-forward and feedback messages do not match, an error signal is generated and the intensity of dyspnea increases. (Adapted from Gillette and Schwartzstein.)

DESCRIPTOR

CHAPTER 5

Dyspnea intensity and quality

41

ASSOCIATION OF QUALITATIVE DESCRIPTORS AND PATHOPHYSIOLOGIC MECHANISMS OF SHORTNESS OF BREATH

Respiratory centers (Respiratory drive)

Chemoreceptors

TABLE 5-1

42

ALGORITHM FOR DYSPNEA PATHOPHYSIOLOGY Dyspnea Respiratory

Gas Exchanger Pulmonary embolism Pneumonia Interstitial lung disease

Pump COPD Asthma Kyphoscoliosis

Cardiovascular

Controller Pregnancy Metabolic acidosis

SECTION II

FIGURE 5-2 Pathophysiology of dyspnea. When confronted with a patient with shortness of breath of unclear cause, it is useful to begin the analysis with a consideration of the broad

Low output Congestive heart failure Myocardial ischemia Constrictive pericarditis

Normal output Deconditioning Obesity Diastolic dysfunction

High output Anemia Hyperthyroidism Arteriovenous shunt

pathophysiologic categories that explain the vast majority of cases. COPD, chronic obstructive pulmonary disease. (Adapted from Schwartzstein and Feller-Kopman.)

Diagnosis of Cardiovascular Disorders

respiratory system can be considered in the context of the controller (stimulation of breathing); the ventilatory pump (the bones and muscles that form the chest wall, the airways, and the pleura); and the gas exchanger (the alveoli, pulmonary vasculature, and surrounding lung parenchyma). Similarly, alterations in the cardiovascular system can be grouped into three categories: conditions associated with high, normal, and low cardiac output (Fig. 5-2).

lung disease and pulmonary vascular congestion may produce dyspnea by direct stimulation of pulmonary receptors. In these cases, relief of hypoxemia typically has only a small impact on the intensity of dyspnea.

Respiratory System Dyspnea

Mild to moderate anemia is associated with breathing discomfort during exercise. Left-to-right intracardiac shunts may lead to high cardiac output and dyspnea, although in their later stages the conditions may be complicated by the development of pulmonary hypertension, which contributes to dyspnea. The breathlessness associated with obesity is probably due to multiple mechanisms, including high cardiac output and impaired ventilatory pump function.

Controller

Acute hypoxemia and hypercapnia are associated with increased activity in the controller. Stimulation of pulmonary receptors, as occurs in acute bronchospasm, interstitial edema, and pulmonary embolism, also leads to hyperventilation and air hunger, as well as a sense of chest tightness in the case of asthma. High altitude, high progesterone states such as pregnancy, and drugs such as aspirin stimulate the controller and can cause dyspnea even when the respiratory system is normal. Ventilatory Pump

Disorders of the airways (e.g., asthma, emphysema, chronic bronchitis, bronchiectasis) lead to increased airway resistance and work of breathing. Hyperinflation further increases the work of breathing and can produce a sense of an inability to get a deep breath. Conditions that stiffen the chest wall, such as kyphoscoliosis, or those that weaken ventilatory muscles, such as myasthenia gravis or the Guillain-Barré syndrome, are also associated with an increased effort to breathe. Large pleural effusions may contribute to dyspnea, both by increasing the work of breathing and by stimulating pulmonary receptors if there is associated atelectasis. Gas Exchanger

Pneumonia, pulmonary edema, and aspiration all interfere with gas exchange. Pulmonary vascular and interstitial

Cardiovascular System Dyspnea High Cardiac Output

Normal Cardiac Output

Cardiovascular deconditioning is characterized by early development of anaerobic metabolism and stimulation of chemoreceptors and metaboreceptors. Diastolic dysfunction—due to hypertension, aortic stenosis, or hypertrophic cardiomyopathy—is an increasingly frequent recognized cause of exercise-induced breathlessness. Pericardial disease, e.g., constrictive pericarditis, is a relatively rare cause of chronic dyspnea. Low Cardiac Output

Diseases of the myocardium resulting from coronary artery disease and nonischemic cardiomyopathies result in a greater left ventricular end-diastolic volume and an elevation of the left ventricular end-diastolic as well as pulmonary capillary pressures. Pulmonary receptors are stimulated by the elevated vascular pressures and resultant interstitial edema, causing dyspnea.

History

Quality of sensation, timing, positional disposition Persistent vs. intermittent

Physical Exam

General appearance: Speak in full sentences? Accessory muscles? Color? Vital signs: Tachypnea? Pulsus paradoxus? Oximetry-evidence of desaturation? Chest: Wheezes, rales, rhonchi, diminished breath sounds? Hyperinflated? Cardiac exam: JVP elevated? Precordial impulse? Gallop? Murmur? Extremities: Edema? Cyanosis?

At this point, diagnosis may be evident—if not, proceed to further evaluation

Chest radiograph Assess cardiac size, evidence of CHF Assess for hyperinflation Assess for pneumonia, interstitial lung disease, pleural effusions

Suspect low cardiac output, myocardial ischemia, or pulmonary vascular disease

Suspect respiratory pump or gas exchange abnormality

Suspect high cardiac output

ECG and echocardiogram to assess left ventricular function and pulmonary artery pressure

Pulmonary function testing—if diffusing capacity reduced, consider CT angiogram to assess for interstitial lung disease and pulmonary embolism

Hematocrit, thyroid function tests

If diagnosis still uncertain, obtain cardiopulmonary exercise test

FIGURE 5-3 An algorithm for the evaluation of the patient with dyspnea. JVP, jugular venous pulse; CHF, congestive heart failure;

ECG, electrocardiogram; CT, computed tomography. (Adapted from Schwartzstein and Feller-Kopman.)

Dyspnea and Pulmonary Edema

(Fig. 5-3) In obtaining a history, the patient should be asked to describe in his/her own words what the discomfort feels like, as well as the effect of position, infections, and environmental stimuli on the dyspnea. Orthopnea is a common indicator of congestive heart failure, mechanical impairment of the diaphragm associated with obesity, or asthma triggered by esophageal reflux. Nocturnal dyspnea suggests congestive heart failure or asthma. Acute, intermittent episodes of dyspnea are more likely to reflect episodes of myocardial ischemia, bronchospasm, or pulmonary embolism, while chronic persistent dyspnea is typical of COPD, and interstitial lung disease. Risk factors for occupational lung disease and for coronary artery disease should be solicited. Left atrial myxoma or hepatopulmonary syndrome should be considered when the patient

43

CHAPTER 5

complains of platypnea, defined as dyspnea in the upright position with relief in the supine position. The physical examination should begin during the interview of the patient. Inability of the patient to speak in full sentences before stopping to get a deep breath suggests a condition that leads to stimulation of the controller or an impairment of the ventilatory pump with reduced vital capacity. Evidence for increased work of breathing (supraclavicular retractions, use of accessory muscles of ventilation, and the tripod position, characterized by sitting with one’s hands braced on the knees) is indicative of disorders of the ventilatory pump, most commonly increased airway resistance or stiff lungs and chest wall. When measuring the vital signs, an accurate assessment of the respiratory rate should be obtained and examination for a pulsus paradoxus carried out (Chap. 22); if it is >10 mmHg, consider the presence of COPD. During the general examination, signs of anemia

Approach to the Patient: DYSPNEA

44 (pale conjunctivae), cyanosis, and cirrhosis (spider

SECTION II Diagnosis of Cardiovascular Disorders

angiomata, gynecomastia) should be sought. Examination of the chest should focus on symmetry of movement; percussion (dullness indicative of pleural effusion, hyper-resonance a sign of emphysema); and auscultation (wheezes, rales, rhonchi, prolonged expiratory phase, diminished breath sounds, which are clues to disorders of the airways, and interstitial edema or fibrosis). The cardiac examination should focus on signs of elevated right heart pressures (jugular venous distention, edema, accentuated pulmonic component to the second heart sound); left ventricular dysfunction (S3 and S4 gallops); and valvular disease (murmurs). When examining the abdomen with the patient in the supine position, it should be noted whether there is paradoxical movement of the abdomen (inward motion during inspiration), a sign of diaphragmatic weakness. Clubbing of the digits may be an indication of interstitial pulmonary fibrosis, and the presence of joint swelling or deformation as well as changes consistent with Raynaud’s disease may be indicative of a collagenvascular process that can be associated with pulmonary disease. Patients with exertional dyspnea should be asked to walk under observation in order to reproduce the symptoms. The patient should be examined for new findings that were not present at rest and for oxygen saturation. A “picture” of the patient while symptomatic may be worth thousands of dollars in laboratory tests. Following the history and physical examination, a chest radiograph should be obtained. The lung volumes should be assessed (hyperinflation indicates obstructive lung disease, low lung volumes suggest interstitial edema or fibrosis, diaphragmatic dysfunction, or impaired chest wall motion). The pulmonary parenchyma should be examined for evidence of interstitial disease and emphysema. Prominent pulmonary vasculature in the upper zones indicates pulmonary venous hypertension, while enlarged central pulmonary arteries suggest pulmonary artery hypertension. An enlarged cardiac silhouette suggests a dilated cardiomyopathy or valvular disease. Bilateral pleural effusions are typical of congestive heart failure and some forms of collagen vascular disease. Unilateral effusions raise the specter of carcinoma and pulmonary embolism but may also occur in heart failure. Computed tomography (CT) of the chest is generally reserved for further evaluation of the lung parenchyma (interstitial lung disease) and possible pulmonary embolism. Laboratory studies should include an electrocardiogram to look for evidence of ventricular hypertrophy and prior myocardial infarction. Echocardiography is indicated in patients in whom systolic dysfunction,

pulmonary hypertension, or valvular heart disease is suspected. DISTINGUISHING CARDIOVASCULAR FROM RESPIRATORY SYSTEM DYSPNEA If a patient has evidence of both

pulmonary and cardiac disease, a cardiopulmonary exercise test should be carried out to determine which system is responsible for the exercise limitation. If, at peak exercise, the patient achieves predicted maximal ventilation, demonstrates an increase in dead space or hypoxemia (oxygen saturation below 90%), or develops bronchospasm, the respiratory system is probably the cause of the problem. Alternatively, if the heart rate is >85% of the predicted maximum, if anaerobic threshold occurs early, if the blood pressure becomes excessively high or drops during exercise, if the O2 pulse (O2 consumption/heart rate, an indicator of stroke volume) falls, or if there are ischemic changes on the electrocardiogram, an abnormality of the cardiovascular system is likely the explanation for the breathing discomfort.

Treatment: DYSPNEA

The first goal is to correct the underlying problem responsible for the symptom. If this is not possible, one attempts to lessen the intensity of the symptom and its effect on the patient’s quality of life. Supplemental O2 should be administered if the resting O2 saturation is ≤90% or if the patient’s saturation drops to these levels with activity. For patients with COPD, pulmonary rehabilitation programs have demonstrated positive effects on dyspnea, exercise capacity, and rates of hospitalization. Studies of anxiolytics and antidepressants have not demonstrated consistent benefit. Experimental interventions—e.g., cold air on the face, chest wall vibration, and inhaled furosemide—to modulate the afferent information from receptors throughout the respiratory system are being studied.

PULMONARY EDEMA MECHANISMS OF FLUID ACCUMULATION The extent to which fluid accumulates in the interstitium of the lung depends on the balance of hydrostatic and oncotic forces within the pulmonary capillaries and in the surrounding tissue. Hydrostatic pressure favors movement of fluid from the capillary into the interstitium. The oncotic pressure, which is determined by the protein concentration in the blood, favors movement of fluid into the vessel. Albumin, the primary protein in the plasma, may be low in conditions such as cirrhosis and nephrotic syndrome. Although hypoalbuminemia favors

Cardiogenic Pulmonary Edema

Noncardiogenic Pulmonary Edema By definition, hydrostatic pressures are normal in noncardiogenic pulmonary edema. Lung water increases due to damage of the pulmonary capillary lining with leakage of proteins and other macromolecules into the tissue; fluid follows the protein as oncotic forces are shifted from the vessel to the surrounding lung tissue.This process is associated with dysfunction of the surfactant lining the alveoli, increased surface forces, and a propensity for the alveoli to collapse at low lung volumes. Physiologically, noncardiogenic pulmonary edema is characterized by intrapulmonary shunt with hypoxemia and decreased pulmonary compliance. Pathologically, hyaline membranes are evident in the alveoli, and inflammation leading to pulmonary fibrosis may be seen. Clinically, the picture ranges from mild dyspnea to respiratory failure. Auscultation of the lungs may be relatively normal despite chest radiographs that show diffuse alveolar infiltrates. CT scans demonstrate that the distribution of alveolar edema is more heterogeneous than was once thought. It is useful to categorize the causes of noncardiogenic pulmonary edema in terms of whether the injury to the lung is likely to result from direct, indirect, or pulmonary

45

COMMON CAUSES OF NONCARDIOGENIC PULMONARY EDEMA Direct Injury to Lung Chest trauma, pulmonary contusion Aspiration Smoke inhalation Pneumonia Oxygen toxicity Pulmonary embolism, reperfusion Hematogenous Injury to Lung Sepsis Pancreatitis Nonthoracic trauma Leukoagglutination reactions Multiple transfusions Intravenous drug use, e.g., heroin Cardiopulmonary bypass Possible Lung Injury Plus Elevated Hydrostatic Pressures High altitude pulmonary edema Neurogenic pulmonary edema Reexpansion pulmonary edema

vascular causes (Table 5-2). Direct injuries are mediated via the airways (e.g., aspiration) or as the consequence of blunt chest trauma. Indirect injury is the consequence of mediators that reach the lung via the blood stream. The third category includes conditions that may be the consequence of acute changes in pulmonary vascular pressures, possibly the result of sudden autonomic discharge in the case of neurogenic and high-altitude pulmonary edema, or sudden swings of pleural pressure, as well as transient damage to the pulmonary capillaries in the case of reexpansion pulmonary edema. Distinguishing Cardiogenic from Noncardiogenic Pulmonary Edema The history is essential for assessing the likelihood of underlying cardiac disease as well as for identification of one of the conditions associated with noncardiogenic pulmonary edema. The physical examination in cardiogenic pulmonary edema is notable for evidence of increased intracardiac pressures (S3 gallop, elevated jugular venous pulse, peripheral edema), and rales and/or wheezes on auscultation of the chest. In contrast, the physical examination in noncardiogenic pulmonary edema is dominated by the findings of the precipitating condition; pulmonary findings may be relatively normal in the early stages. The chest radiograph in cardiogenic pulmonary edema typically shows an enlarged cardiac silhouette, vascular redistribution, interstitial thickening, and perihilar alveolar infiltrates; pleural effusions are

Dyspnea and Pulmonary Edema

(See also Chap. 28) Cardiac abnormalities that lead to an increase in pulmonary venous pressure shift the balance of forces between the capillary and the interstitium. Hydrostatic pressure is increased and fluid exits the capillary at an increased rate, resulting in interstitial and, in more severe cases, alveolar edema. The development of pleural effusions may further compromise respiratory system function and contribute to breathing discomfort. Early signs of pulmonary edema include exertional dyspnea and orthopnea. Chest radiographs show peribronchial thickening, prominent vascular markings in the upper lung zones, and Kerley B lines. As the pulmonary edema worsens, alveoli fill with fluid; the chest radiograph shows patchy alveolar filling, typically in a perihilar distribution, which then progresses to diffuse alveolar infiltrates. Increasing airway edema is associated with rhonchi and wheezes.

TABLE 5-2

CHAPTER 5

movement of fluid into the tissue for any given hydrostatic pressure in the capillary, it is usually not sufficient by itself to cause interstitial edema. In a healthy individual, the tight junctions of the capillary endothelium are impermeable to proteins, and the lymphatics in the tissue carry away the small amounts of protein that may leak out; together these factors result in an oncotic force that maintains fluid in the capillary. Disruption of the endothelial barrier, however, allows protein to escape the capillary bed and enhances the movement of fluid into the tissue of the lung.

46 common. In noncardiogenic pulmonary edema, heart

SECTION II

size is normal, alveolar infiltrates are distributed more uniformly throughout the lungs, and pleural effusions are uncommon. Finally, the hypoxemia of cardiogenic pulmonary edema is due largely to ventilation-perfusion mismatch and responds to the administration of supplemental oxygen. In contrast, hypoxemia in noncardiogenic pulmonary edema is due primarily to intrapulmonary shunting and typically persists despite high concentrations of inhaled O2. FURTHER READINGS

Diagnosis of Cardiovascular Disorders

AARON SD et al: Overdiagnosis of asthma in obese and nonobese adults. CMAJ 179:1121, 2008 ABIDOV A et al: Prognostic significance of dyspnea in patients referred for cardiac stress testing. N Engl J Med 353:1889, 2005

BANZETT RB et al: The affective dimension of laboratory dyspnea: Air hunger is more unpleasant than work/effort. Am J Respir Crit Care Med 177:1384, 2008 Dyspnea mechanisms, assessment, and management: A consensus statement.Am Rev Resp Crit Care Med 159:321, 1999 G ILLETTE MA, S CHWARTZSTEIN RM: Mechanisms of dyspnea, in Supportive Care in Respiratory Disease, SH Ahmedzai and MF Muer (eds). Oxford, Oxford University Press, 2005 MAHLER DA et al: Descriptors of breathlessness in cardiorespiratory diseases.Am J Respir Crit Care Med 154:1357, 1996 ———, O’DONNELL DE (eds): Dyspnea: Mechanisms, Measurement, and Management. New York, Marcel Dekker, 2005 SCHWARTZSTEIN RM. The language of dyspnea, in Dyspnea: Mechanisms, Measurement, and Management, DA Mahler and DE O’Donnell (eds). New York, Marcel Dekker, 2005 ———, FELLER-KOPMAN D: Shortness of breath, in Primary Care Cardiology, 2d ed, E Braunwald and L Goldman (eds). Philadelphia:WB Saunders, 2003

CHAPTER 6

HYPOXIA AND CYANOSIS Eugene Braunwald

■ Hypoxia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Effects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Causes of Hypoxia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Adaptation to Hypoxia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 ■ Cyanosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 Differential Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 ■ Clubbing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

including glycolytic enzymes such as phosphoglycerate kinase and phosphofructokinase, as well as the glucose transporters GLUT-1 and GLUT-2; and by growth factors, such as vascular endothelial growth factor (VEGF) and erythropoietin, which enhance erythrocyte production. During hypoxia systemic arterioles dilate, at least in part, by opening of KATP channels in vascular smoothmuscle cells due to the hypoxia-induced reduction in ATP concentration. By contrast, in pulmonary vascular smooth-muscle cells, inhibition of K+ channels causes depolarization which, in turn, activates voltage-gated Ca2+ channels raising the cytosolic [Ca2+] and causing smooth-muscle cell contraction. Hypoxiainduced pulmonary arterial constriction shunts blood away from poorly ventilated toward better-ventilated portions of the lung; however, it also increases pulmonary vascular resistance and right ventricular afterload.

HYPOXIA The fundamental task of the cardiorespiratory system is to deliver O2 (and substrates) to the cells and to remove CO2 (and other metabolic products) from them. Proper maintenance of this function depends on intact cardiovascular and respiratory systems, an adequate number of red blood cells and hemoglobin, and a supply of inspired gas containing adequate O2.

EFFECTS Decreased O2 availability to cells results in an inhibition of the respiratory chain and increased anaerobic glycolysis. This switch from aerobic to anaerobic metabolism, Pasteur’s effect, maintains some, albeit markedly reduced, adenosine triphosphate (ATP) production. In severe hypoxia, when ATP production is inadequate to meet the energy requirements of ionic and osmotic equilibrium, cell membrane depolarization leads to uncontrolled Ca2+ influx and activation of Ca2+-dependent phospholipases and proteases. These events, in turn, cause cell swelling and ultimately cell necrosis. The adaptations to hypoxia are mediated, in part, by the upregulation of genes encoding a variety of proteins,

Effects on the Central Nervous System Changes in the central nervous system, particularly the higher centers, are especially important consequences of hypoxia. Acute hypoxia causes impaired judgment, motor incoordination, and a clinical picture resembling acute

47

48 alcoholism. High-altitude illness is characterized by

SECTION II

headache secondary to cerebral vasodilatation, and by gastrointestinal symptoms, dizziness, insomnia, and fatigue, or somnolence. Pulmonary arterial and sometimes venous constriction cause capillary leakage and high-altitude pulmonary edema (HAPE) (Chap. 5), which intensifies hypoxia and can initiate a vicious circle. Rarely, highaltitude cerebral edema (HACE) develops. This is manifest by severe headache and papilledema and can cause coma. As hypoxia becomes more severe, the centers of the brainstem are affected, and death usually results from respiratory failure.

CAUSES OF HYPOXIA

Diagnosis of Cardiovascular Disorders

Respiratory Hypoxia When hypoxia occurs consequent to respiratory failure, PaO2 declines, and when respiratory failure is persistent, the hemoglobin-oxygen (Hb-O2) dissociation curve is displaced to the right, with greater quantities of O2 released at any level of tissue PO2. Arterial hypoxemia, i.e., a reduction of O2 saturation of arterial blood (SaO2), and consequent cyanosis are likely to be more marked when such depression of PaO2 results from pulmonary disease than when the depression occurs as the result of a decline in the fraction of oxygen in inspired air (FIO2). In the latter situation, PaCO2 falls secondary to anoxiainduced hyperventilation and the Hb-O2 dissociation curve is displaced to the left, limiting the decline in SaO2 at any level of PaO2. The most common cause of respiratory hypoxia is ventilation-perfusion mismatch resulting from perfusion of poorly ventilated alveoli. Respiratory hypoxemia may also be caused by hypoventilation, and it is then associated with an elevation of PaCO2.The two forms of respiratory hypoxia are usually correctable by inspiring 100% O2 for several minutes. A third cause is shunting of blood across the lung from the pulmonary arterial to the venous bed (intrapulmonary right-to-left shunting) by perfusion of nonventilated portions of the lung, as in pulmonary atelectasis or through pulmonary arteriovenous connections.The low PaO2 in this situation is correctable only in part by an FIO2 of 100%. Hypoxia Secondary to High Altitude As one ascends rapidly to 3000 m (∼10,000 ft), the reduction of the O2 content of inspired air (FIO2) leads to a decrease in alveolar PO2 to about 60 mmHg, and a condition termed high-altitude illness develops (see earlier). At higher altitudes, arterial saturation declines rapidly and symptoms become more serious; and at 5000 m, unacclimatized individuals usually cease to be able to function normally.

Hypoxia Secondary to Right-to-Left Extrapulmonary Shunting From a physiologic viewpoint, this cause of hypoxia resembles intrapulmonary right-to-left shunting but is caused by congenital cardiac malformations such as tetralogy of Fallot, transposition of the great arteries, and Eisenmenger’s syndrome (Chap. 19). As in pulmonary right-to-left shunting, the PaO2 cannot be restored to normal with inspiration of 100% O2. Anemic Hypoxia A reduction in hemoglobin concentration of the blood is attended by a corresponding decline in the O2-carrying capacity of the blood. Although the PaO2 is normal in anemic hypoxia, the absolute quantity of O2 transported per unit volume of blood is diminished. As the anemic blood passes through the capillaries and the usual quantity of O2 is removed from it, the PO2 and saturation in the venous blood decline to a greater degree than normal. Carbon Monoxide (CO) Intoxication Hemoglobin that is combined with CO [carboxyhemoglobin (COHb)] is unavailable for O2 transport. In addition, the presence of COHb shifts the Hb-O2 dissociation curve to the left so that O2 is unloaded only at lower tensions, contributing further to tissue hypoxia. Circulatory Hypoxia As in anemic hypoxia, the PaO2 is usually normal, but venous and tissue PO2 values are reduced as a consequence of reduced tissue perfusion and greater tissue O2 extraction. This pathophysiology leads to an increased arterial–mixed venous O2 difference, or (a – v) gradient. Generalized circulatory hypoxia occurs in heart failure (Chap. 17) and in most forms of shock. Specific Organ Hypoxia Localized circulatory hypoxia may occur consequent to decreased perfusion secondary to organic arterial obstruction, as in localized atherosclerosis in any vascular bed, or as a consequence of vasoconstriction, as observed in Raynaud’s phenomenon (Chap. 39). Localized hypoxia may also result from venous obstruction and the resultant expansion of interstitial fluid causing arterial compression and, thereby, reduction of arterial inflow. Edema, which increases the distance through which O2 must diffuse before it reaches cells, can also cause localized hypoxia. In an attempt to maintain adequate perfusion to more vital organs in patients with reduced cardiac output secondary to heart failure or hypovolemic shock, vasoconstriction may reduce perfusion in the limbs and skin, causing hypoxia of these regions.

Increased O2 Requirements

Cyanide and several other similarly acting poisons cause cellular hypoxia.The tissues are unable to utilize O2, and as a consequence, the venous blood tends to have a high O2 tension. This condition has been termed histotoxic hypoxia.

ADAPTATION TO HYPOXIA An important component of the respiratory response to hypoxia originates in special chemosensitive cells in the carotid and aortic bodies and in the respiratory center in the brainstem. The stimulation of these cells by hypoxia increases ventilation, with a loss of CO2, and can lead to respiratory alkalosis.When combined with the metabolic acidosis resulting from the production of lactic acid, the serum bicarbonate level declines. With the reduction of PaO2, cerebrovascular resistance decreases and cerebral blood flow increases in an attempt to maintain O2 delivery to the brain. However, when the reduction of PaO2 is accompanied by hyperventilation and a reduction of PaCO2, cerebrovascular resistance rises, cerebral blood flow falls, and hypoxia is intensified. The diffuse, systemic vasodilation that occurs in generalized hypoxia raises the cardiac output. In patients with underlying heart disease, the requirements of peripheral tissues for an increase of cardiac output with hypoxia may precipitate congestive heart failure. In patients with ischemic heart disease, a reduced PaO2 may intensify

CYANOSIS Cyanosis refers to a bluish color of the skin and mucous membranes resulting from an increased quantity of reduced hemoglobin, or of hemoglobin derivatives, in the small blood vessels of those areas. It is usually most marked in the lips, nail beds, ears, and malar eminences. Cyanosis, especially if developed recently, is more commonly detected by a family member than the patient. The florid skin characteristic of polycythemia vera must be distinguished from the true cyanosis discussed here. A cherry-colored flush, rather than cyanosis, is caused by carboxyhemoglobin (COHb). The degree of cyanosis is modified by the color of the cutaneous pigment and the thickness of the skin, as well as by the state of the cutaneous capillaries. The accurate clinical detection of the presence and degree of cyanosis is difficult, as proved by oximetric studies. In some instances, central cyanosis can be detected reliably when the SaO2 has decreased to 85%; in others, particularly in dark-skinned persons, it may not be detected until it has decreased to 75%. In the latter case, examination of the mucous membranes in the oral cavity and the conjunctivae rather than examination of the skin is more helpful in the detection of cyanosis. The increase in the quantity of reduced hemoglobin in the mucocutaneous vessels that produces cyanosis may be brought about either by an increase in the quantity of venous blood as a result of dilation of the venules and venous ends of the capillaries or by a reduction in the SaO2 in the capillary blood. In general, cyanosis becomes apparent when the concentration of reduced hemoglobin in capillary blood exceeds 40 g/L (4 g/dL). It is the absolute, rather than the relative, quantity of reduced hemoglobin that is important in producing cyanosis. Thus, in a patient with severe anemia, the relative quantity of reduced hemoglobin in the venous blood may be very large when considered in relation to the total quantity of hemoglobin in the blood. However, since the concentration of the latter is markedly reduced,

Hypoxia and Cyanosis

Improper Oxygen Utilization

CHAPTER 6

If the O2 consumption of tissues is elevated without a corresponding increase in perfusion, tissue hypoxia ensues and the PO2 in venous blood declines. Ordinarily, the clinical picture of patients with hypoxia due to an elevated metabolic rate, as in fever or thyrotoxicosis, is quite different from that in other types of hypoxia; the skin is warm and flushed owing to increased cutaneous blood flow that dissipates the excessive heat produced, and cyanosis is usually absent. Exercise is a classic example of increased tissue O2 requirements. These increased demands are normally met by several mechanisms operating simultaneously: (1) increasing the cardiac output and ventilation and, thus, O2 delivery to the tissues; (2) preferentially directing the blood to the exercising muscles by changing vascular resistances in the circulatory beds of exercising tissues, directly and/or reflexly; (3) increasing O2 extraction from the delivered blood and widening the arteriovenous O2 difference; and (4) reducing the pH of the tissues and capillary blood, shifting the Hb-O2 curve to the right and unloading more O2 from hemoglobin. If the capacity of these mechanisms is exceeded, then hypoxia, especially of the exercising muscles, will result.

myocardial ischemia and further impair left ventricular 49 function. One of the important mechanisms of compensation for chronic hypoxia is an increase in the hemoglobin concentration and in the number of red blood cells in the circulating blood, i.e., the development of polycythemia secondary to erythropoietin production. In persons with chronic hypoxemia secondary to prolonged residence at a high altitude (4200 m, >13,000 ft), a condition termed chronic mountain sickness develops. It is characterized by a blunted respiratory drive, reduced ventilation, erythrocytosis, cyanosis, weakness, right ventricular enlargement secondary to pulmonary hypertension, and even stupor.

50 the absolute quantity of reduced hemoglobin may still

SECTION II Diagnosis of Cardiovascular Disorders

be small, and, therefore, patients with severe anemia and even marked arterial desaturation may not display cyanosis. Conversely, the higher the total hemoglobin content, the greater is the tendency toward cyanosis; thus, patients with marked polycythemia tend to be cyanotic at higher levels of SaO2 than patients with normal hematocrit values. Likewise, local passive congestion, which causes an increase in the total quantity of reduced hemoglobin in the vessels in a given area, may cause cyanosis. Cyanosis is also observed when nonfunctional hemoglobin, such as methemoglobin or sulfhemoglobin, is present in blood. Cyanosis may be subdivided into central and peripheral types. In the central type, the SaO2 is reduced or an abnormal hemoglobin derivative is present, and the mucous membranes and skin are both affected. Peripheral cyanosis is due to a slowing of blood flow and abnormally great extraction of O2 from normally saturated arterial blood. It results from vasoconstriction and diminished peripheral blood flow, such as occurs in cold exposure, shock, congestive failure, and peripheral vascular disease. Often in these conditions, the mucous membranes of the oral cavity or those beneath the tongue may be spared. Clinical differentiation between central and peripheral cyanosis may not always be simple, and in conditions such as cardiogenic shock with pulmonary edema there may be a mixture of both types.

DIFFERENTIAL DIAGNOSIS Central Cyanosis (Table 6-1) Decreased SaO2 results from a marked reduction in the PaO2. This reduction may be brought about by a decline in the FIO2 without sufficient compensatory alveolar hyperventilation to maintain alveolar PO2. Cyanosis usually becomes manifest in an ascent to an altitude of 4000 m (13,000 ft). Seriously impaired pulmonary function, through perfusion of unventilated or poorly ventilated areas of the lung or alveolar hypoventilation, is a common cause of central cyanosis.The condition may occur acutely, as in extensive pneumonia or pulmonary edema, or chronically with chronic pulmonary diseases (e.g., emphysema). In the latter situation, secondary polycythemia is generally present and clubbing of the fingers (see later) may occur. Another cause of reduced SaO2 is shunting of systemic venous blood into the arterial circuit. Certain forms of congenital heart disease are associated with cyanosis on this basis (see above and Chap. 19). Pulmonary arteriovenous fistulae may be congenital or acquired, solitary or multiple, microscopic or massive.The severity of cyanosis produced by these fistulae depends on their size and number. They occur with some frequency in hereditary hemorrhagic telangiectasia. SaO2 reduction and cyanosis may also occur in some patients with

TABLE 6-1 CAUSES OF CYANOSIS Central Cyanosis Decreased arterial oxygen saturation Decreased atmospheric pressure—high altitude Impaired pulmonary function Alveolar hypoventilation Uneven relationships between pulmonary ventilation and perfusion (perfusion of hypoventilated alveoli) Impaired oxygen diffusion Anatomic shunts Certain types of congenital heart disease Pulmonary arteriovenous fistulas Multiple small intrapulmonary shunts Hemoglobin with low affinity for oxygen Hemoglobin abnormalities Methemoglobinemia—hereditary, acquired Sulfhemoglobinema—acquired Carboxyhemoglobinemia (not true cyanosis) Peripheral Cyanosis Reduced cardiac output Cold exposure Redistribution of blood flow from extremities Arterial obstruction Venous obstruction

cirrhosis, presumably as a consequence of pulmonary arteriovenous fistulae or portal vein–pulmonary vein anastomoses. In patients with cardiac or pulmonary right-to-left shunts, the presence and severity of cyanosis depend on the size of the shunt relative to the systemic flow as well as on the Hb-O2 saturation of the venous blood. With increased extraction of O2 from the blood by the exercising muscles, the venous blood returning to the right side of the heart is more unsaturated than at rest, and shunting of this blood intensifies the cyanosis. Secondary polycythemia occurs frequently in patients with arterial O2 unsaturation and contributes to the cyanosis. Cyanosis can be caused by small quantities of circulating methemoglobin and by even smaller quantities of sulfhemoglobin. Although they are uncommon causes of cyanosis, these abnormal oxyhemoglobin derivatives should be sought by spectroscopy when cyanosis is not readily explained by malfunction of the circulatory or respiratory systems. Generally, digital clubbing does not occur with them. Peripheral Cyanosis Probably the most common cause of peripheral cyanosis is the normal vasoconstriction resulting from exposure to cold air or water. When cardiac output is reduced,

Certain features are important in arriving at the cause of cyanosis: 1. It is important to ascertain the time of onset of cyanosis. Cyanosis present since birth or infancy is usually due to congenital heart disease. 2. Central and peripheral cyanosis must be differentiated. Evidences of disorders of the respiratory or cardiovascular systems are helpful. Massage or gentle warming of a cyanotic extremity will increase peripheral blood flow and abolish peripheral, but not central, cyanosis. 3. The presence or absence of clubbing of the digits (see later) should be ascertained. The combination of cyanosis and clubbing is frequent in patients with congenital heart disease and right-to-left shunting, and is seen occasionally in patients with pulmonary disease such as lung abscess or pulmonary arteriovenous fistulae. In contrast, peripheral cyanosis or acutely developing central cyanosis is not associated with clubbed digits. 4. PaO2 and SaO2 should be determined, and in patients with cyanosis in whom the mechanism is obscure, spectroscopic examination of the blood performed to look for abnormal types of hemoglobin (critical in the differential diagnosis of cyanosis).

CLUBBING The selective bulbous enlargement of the distal segments of the fingers and toes due to proliferation of connective tissue, particularly on the dorsal surface, is termed clubbing;

Hypoxia and Cyanosis

Approach to the Patient: CYANOSIS

there is also increased sponginess of the soft tissue at the 51 base of the nail. Clubbing may be hereditary, idiopathic, or acquired and associated with a variety of disorders, including cyanotic congenital heart disease (see earlier), infective endocarditis, and a variety of pulmonary conditions (among them primary and metastatic lung cancer, bronchiectasis, lung abscess, cystic fibrosis, and mesothelioma), as well as with some gastrointestinal diseases (including inflammatory bowel disease and hepatic cirrhosis). In some instances it is occupational, e.g., in jackhammer operators. Clubbing in patients with primary and metastatic lung cancer, mesothelioma, bronchiectasis, and hepatic cirrhosis may be associated with hypertrophic osteoarthropathy. In this condition, the subperiosteal formation of new bone in the distal diaphyses of the long bones of the extremities causes pain and symmetric arthritis-like changes in the shoulders, knees, ankles, wrists, and elbows. The diagnosis of hypertrophic osteoarthropathy may be confirmed by bone radiographs.Although the mechanism of clubbing is unclear, it appears to be secondary to a humoral substance that causes dilation of the vessels of the fingertip.

CHAPTER 6

cutaneous vasoconstriction occurs as a compensatory mechanism so that blood is diverted from the skin to more vital areas such as the central nervous system and heart, and cyanosis of the extremities may result even though the arterial blood is normally saturated. Arterial obstruction to an extremity, as with an embolus, or arteriolar constriction, as in cold-induced vasospasm (Raynaud’s phenomenon, Chap. 39), generally results in pallor and coldness, and there may be associated cyanosis. Venous obstruction, as in thrombophlebitis, dilates the subpapillary venous plexuses and thereby intensifies cyanosis.

FURTHER READINGS BANSAL S et al: Sodium retention in heart failure and cirrhosis. Potential role of natriuretic doses of mineralocorticoid antagonist Circ Hear Fail 2:370, 2009 FAWCETT RS et al: Nail abnormalities: Clues to systemic disease. Am Fam Physician 69:1417, 2004 GIORDANO FJ: Oxygen, oxidative stress, hypoxia, and heart failure. J Clin Invest 115:500, 2005 GRIFFEY RT et al: Cyanosis. J Emerg Med 18:369, 2000 HACKETT PH, ROACH RC: Current concepts: High altitude illness. N Engl J Med 345:107, 2001 LEVY MM: Pathophysiology of oxygen delivery in respiratory failure. Chest 128(Suppl 2):547S, 2005 MCCULLOUGH JC: Renal disorders and heart disease, in Braunwald’s Heart Disease, 8th ed, P. Libby et al (eds). Philadelphia, Saunders Elsevier, 2008 MICHIELS C: Physiological and pathological responses to hypoxia. Am J Pathol 164:1875, 2004 SCHRIER RW: Decreased effective blood volume in edematous disorders: What does this mean? J Am Soc Nephrol 18:2028, 2007 SEMENZA GL: Involvement of oxygen-sensing pathways in physiological and pathological erythropoiesis. Blood, e-published, 2009 SKoRECKI KL et al: Extracellular fluid and edema formation, in Brenner and Rector’s The Kidney, 8th ed, Philadelphia, Elsevier, 2008 SPICKNALL KE, ZIRWAS MJ: English JC 3rd. Clubbing: an update on diagnosis, differential diagnosis, pathophysiology, and clinical relevance. J Am Acad Dermatol 52:1020, 2005 TSAI BM et al: Hypoxic pulmonary vasoconstriction in cardiothoracic surgery: Basic mechanisms to potential therapies. Ann Thorac Surg 78:360, 2004

CHAPTER 7

EDEMA Eugene Braunwald

■

Joseph Loscalzo

Pathogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 Clinical Causes of Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54 ■ Differential Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Localized Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Generalized Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Distribution of Edema . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58 Additional Factors in Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . 58 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Edema is defined as a clinically apparent increase in the interstitial fluid volume, which may expand by several liters before the abnormality is evident.Therefore, a weight gain of several kilograms usually precedes overt manifestations of edema, and a similar weight loss from diuresis can be induced in a slightly edematous patient before “dry weight” is achieved. Anasarca refers to gross, generalized edema. Ascites and hydrothorax refer to accumulation of excess fluid in the peritoneal and pleural cavities, respectively, and are considered to be special forms of edema. Depending on its cause and mechanism, edema may be localized or have a generalized distribution; it is recognized in its generalized form by puffiness of the face, which is most readily apparent in the periorbital areas, and by the persistence of an indentation of the skin following pressure; this is known as “pitting” edema. In its more subtle form, edema may be detected by noting that after the stethoscope is removed from the chest wall, the rim of the bell leaves an indentation on the skin of the chest for a few minutes. When the ring on a finger fits more snugly than in the past or when a patient complains of difficulty in putting on shoes, particularly in the evening, edema may be present.

Starling Forces The forces that regulate the disposition of fluid between the two components of the extracellular compartment are frequently referred to as the Starling forces. The hydrostatic pressure within the vascular system and the colloid oncotic pressure in the interstitial fluid tend to promote movement of fluid from the vascular to the extravascular space. On the other hand, the colloid oncotic pressure contributed by plasma proteins and the hydrostatic pressure within the interstitial fluid, referred to as the tissue tension, promote the movement of fluid into the vascular compartment. As a consequence of these forces, there is a movement of water and diffusible solutes from the vascular space at the arteriolar end of the capillaries. Fluid is returned from the interstitial space into the vascular system at the venous end of the capillaries and by way of the lymphatics. Unless these channels are obstructed, lymph flow rises with increases in net movement of fluid from the vascular compartment to the interstitium. The flows are usually balanced so that a steady state exists in the sizes of the intravascular and interstitial compartments, and, yet, a large exchange between them occurs. However, should either the hydrostatic or oncotic pressure gradient be altered significantly, a further net movement of fluid between the two components of the extracellular space will take place. The development of edema, then, depends on one or more alterations in the Starling forces so that there is

PATHOGENESIS About one-third of total-body water is confined to the extracellular space. Approximately 75% of the extracellular space is interstitial fluid and the remainder is the plasma.

52

Edema may also result from damage to the capillary endothelium, which increases its permeability and permits the transfer of protein into the interstitial compartment. Injury to the capillary wall can result from drugs, viral or bacterial agents, and thermal or mechanical trauma. Increased capillary permeability may also be a consequence of a hypersensitivity reaction and is characteristic of immune injury. Damage to the capillary endothelium is presumably responsible for inflammatory edema, which is usually nonpitting, localized, and accompanied by other signs of inflammation—redness, heat, and tenderness. Reduction of Effective Arterial Volume In many forms of edema, the effective arterial blood volume, a parameter that represents the filling of the arterial tree, is reduced. Underfilling of the arterial tree may be caused by a reduction of cardiac output and/or systemic vascular resistance.As a consequence of underfilling, a series of physiologic responses designed to restore the effective arterial volume to normal are set into motion. A key element of these responses is the retention of salt and, therefore, of water, ultimately leading to edema. Renal Factors and the Renin-AngiotensinAldosterone (RAA) System In the final analysis, renal retention of Na+ is central to the development of generalized edema. The diminished renal blood flow characteristic of states in which the effective arterial blood volume is reduced is translated by the renal juxtaglomerular cells (specialized myoepithelial cells surrounding the afferent arteriole) into a signal for increased renin release. Renin is an enzyme with a molecular mass of about 40,000 Da that acts on its substrate, angiotensinogen, an α2-globulin synthesized by the liver, to release angiotensin I (AI), a decapeptide, which is broken down to angiotensin II (AII), an octapeptide.

Edema

Capillary Damage

AII has generalized vasoconstrictor properties; it is espe- 53 cially active on the efferent arterioles.This efferent arteriolar constriction reduces the hydrostatic pressure in the peritubular capillaries, while the increased filtration fraction raises the colloid osmotic pressure in these vessels, thereby enhancing salt and water reabsorption in the proximal tubule as well as in the ascending limb of the loop of Henle. The RAA system has long been recognized as a hormonal system; however, it also operates locally. Intrarenally produced AII contributes to glomerular efferent arteriolar constriction, and this “tubuloglomerular feedback” causes salt and water retention. These renal effects of AII are mediated by activation of AII type 1 receptors, which can be blocked by specific antagonists [angiotensin receptor blockers (ARBs)]. The mechanisms responsible for the increased release of renin when renal blood flow is reduced include: (1) a baroreceptor response in which reduced renal perfusion results in incomplete filling of the renal arterioles and diminished stretch of the juxtaglomerular cells, a signal that increases the elaboration and/or release of renin; (2) reduced glomerular filtration, which lowers the NaCl load reaching the distal renal tubules and the macula densa, cells in the distal convoluted tubules that act as chemoreceptors and that signal the neighboring juxtaglomerular cells to secrete renin; and (3) activation of the β-adrenergic receptors in the juxtaglomerular cells by the sympathetic nervous system and by circulating catecholamines, which also stimulates renin release. The three mechanisms generally act in concert to enhance Na+ retention and, thereby, contribute to the formation of edema. AII that enters the systemic circulation stimulates the production of aldosterone by the zona glomerulosa of the adrenal cortex. Aldosterone, in turn, enhances Na+ reabsorption (and K+ excretion) by the collecting tubule. In patients with heart failure, not only is aldosterone secretion elevated but the biologic half-life of aldosterone is prolonged, which increases further the plasma level of the hormone. A depression of hepatic blood flow, especially during exercise, is responsible for reduced hepatic catabolism of aldosterone. The activation of the RAA system is most striking in the early phase of acute, severe heart failure and is less intense in patients with chronic, stable, compensated heart failure. Increased quantities of aldosterone are secreted in heart failure and in other edematous states, and blockade of the action of aldosterone by spironolactone (an aldosterone antagonist) or amiloride (a blocker of epithelial Na+ channels) often induces a moderate diuresis in edematous states.Yet, persistently augmented levels of aldosterone (or other mineralocorticoids) alone do not always promote accumulation of edema, as witnessed by the lack of striking fluid retention in most instances of primary aldosteronism. Furthermore, although normal

CHAPTER 7

increased flow of fluid from the vascular system into the interstitium or into a body cavity. Edema due to an increase in capillary pressure may result from an elevation of venous pressure due to obstruction to venous and/or lymphatic drainage. An increase in capillary pressure may be generalized, as occurs in congestive heart failure (see below).The Starling forces may also be imbalanced when the colloid oncotic pressure of the plasma is reduced, owing to any factor that may induce hypoalbuminemia, such as severe malnutrition, liver disease, loss of protein into the urine or into the gastrointestinal tract, or a severe catabolic state. Edema may be localized to one extremity when venous pressure is elevated due to unilateral thrombophlebitis (see later in the chapter).

54 individuals retain some NaCl and water with the admin-

SECTION II Diagnosis of Cardiovascular Disorders

istration of potent mineralocorticoids, such as deoxycorticosterone acetate or fludrocortisone, this accumulation is self-limiting, despite continued exposure to the steroid, a phenomenon known as mineralocorticoid escape. The failure of normal individuals who receive large doses of mineralocorticoids to accumulate large quantities of extracellular fluid and to develop edema is probably a consequence of an increase in glomerular filtration rate (pressure natriuresis) and the action of natriuretic substance(s) (see later).The continued secretion of aldosterone may be more important in the accumulation of fluid in edematous states because patients with edema secondary to heart failure, nephrotic syndrome, and hepatic cirrhosis are generally unable to repair the deficit in effective arterial blood volume. As a consequence, they do not develop pressure natriuresis.

BNP are elevated in congestive heart failure and in cirrhosis with ascites, but obviously not sufficiently to prevent edema formation. In addition, in edematous states there is abnormal resistance to the actions of natriuretic peptides.

CLINICAL CAUSES OF EDEMA Obstruction of Venous (and Lymphatic) Drainage of a Limb

The secretion of AVP occurs in response to increased intracellular osmolar concentration, and by stimulating V2 receptors, AVP increases the reabsorption of free water in the renal distal tubule and collecting duct, thereby increasing total-body water. Circulating AVP is elevated in many patients with heart failure secondary to a nonosmotic stimulus associated with decreased effective arterial volume. Such patients fail to show the normal reduction of AVP with a reduction of osmolality, contributing to edema formation and hyponatremia.

In this condition the hydrostatic pressure in the capillary bed upstream (proximal) to the obstruction increases so that an abnormal quantity of fluid is transferred from the vascular to the interstitial space. Since the alternative route (i.e., the lymphatic channels) may also be obstructed or maximally filled, an increased volume of interstitial fluid in the limb develops, i.e., there is trapping of fluid in the extremity.Tissue tension rises in the affected limb until it counterbalances the primary alterations in the Starling forces, at which time no further fluid accumulates. The net effect is a local increase in the volume of interstitial fluid, causing local edema. The displacement of fluid into a limb may occur at the expense of the blood volume in the remainder of the body, thereby reducing effective arterial blood volume and leading to the retention of NaCl and H2O until the deficit in plasma volume has been corrected. This sequence occurs in ascites and hydrothorax, in which fluid is trapped or accumulates in the cavitary space, depleting the intravascular volume and leading to secondary salt and fluid retention.

Endothelin

Congestive Heart Failure

This potent peptide vasoconstrictor is released by endothelial cells; its concentration is elevated in heart failure and contributes to renal vasoconstriction, Na+ retention, and edema in heart failure.

(See also Chap. 17) In this disorder the impaired systolic emptying of the ventricle(s) and/or the impairment of ventricular relaxation promotes an accumulation of blood in the venous circulation at the expense of the effective arterial volume, and the aforementioned sequence of events (Fig. 7-1) is initiated. In mild heart failure, a small increment of total blood volume may repair the deficit of arterial volume and establish a new steady state. Through the operation of Starling’s law of the heart, an increase in ventricular diastolic volume promotes a more forceful contraction and may thereby restore the cardiac output. However, if the cardiac disorder is more severe, fluid retention continues, and the increment in blood volume accumulates in the venous circulation. With reduction in cardiac output, a decrease in baroreflex-mediated inhibition of the vasomotor center activates renal vasoconstrictor nerves and the RAA system, causing Na+ and H2O retention. Incomplete ventricular emptying (systolic heart failure) and/or inadequate ventricular relaxation (diastolic heart failure) both lead to an elevation of ventricular diastolic pressure. If the impairment of cardiac function primarily involves the right ventricle, pressures in the

Arginine Vasopressin (AVP)

Natriuretic Peptides Atrial distention and/or a Na+ load cause release into the circulation of atrial natriuretic peptide (ANP), a polypeptide; a high-molecular-weight precursor of ANP is stored in secretory granules within atrial myocytes. Release of ANP causes (1) excretion of sodium and water by augmenting glomerular filtration rate, inhibiting sodium reabsorption in the proximal tubule, and inhibiting release of renin and aldosterone; and (2) arteriolar and venous dilation by antagonizing the vasoconstrictor actions of AII, AVP, and sympathetic stimulation.Thus, ANP has the capacity to oppose Na+ retention and arterial pressure elevation in hypervolemic states. The closely related brain natriuretic peptide (BNP) is stored primarily in ventricular myocardium and is released when ventricular diastolic pressure rises. Its actions are similar to those of ANP. Circulating levels of ANP and

55

ALGORITHM ON DEVELOPMENT OF EDEMA Heart failure Central venous and atrial pressure

Malnutrition, hepatic synthesis, nephrotic syndrome, G.I. loss

Ascites, other effusions, venous or lymphatic obstruction

ANP

Blood volume

1° Renal failure

A-V fistula

Oncotic pressure

Capillary pressure

CHAPTER 7

Transudation Cardiac output

Plasma volume

RPF filtration fraction Interstitial volume

Proximal tubular reabsorption of Na and H2O

Effective arterial blood volume

GFR

ADH

Renin Angiotensin II

GFR/Nephron

Proximal tubular reabsorption Na + H2O

Aldosterone Distal tubular Na reabsorption

Distal H2O retention

Renal retention of Na and H2O

Plasma volume Transudation

Interstitial volume

Edema

FIGURE 7-1 Sequence of events leading to the formation and retention of salt and water and the development of edema. ANP, atrial natriuretic peptide; RPF, renal plasma flow; GFR,

systemic veins and capillaries rise, augmenting the transudation of fluid into the interstitial space and enhancing the likelihood of peripheral edema. The elevated systemic venous pressure is transmitted to the thoracic duct with consequent reduction of lymph drainage, further increasing the accumulation of edema. If the impairment of cardiac function (incomplete ventricular emptying and/or inadequate relaxation) involves the left ventricle primarily, then, pulmonary venous and capillary pressures rise. Pulmonary artery pressure rises and this, in turn, interferes with the emptying of the right ventricle, leading to an elevation of right ventricular diastolic and of central and systemic venous pressures, thereby enhancing the likelihood of the formation of peripheral edema. The elevation of pulmonary capillary pressure may cause pulmonary edema, which impairs gas exchange. The resultant hypoxemia

glomerular filtration rate; ADH, antidiuretic hormone. Inhibitory influences are shown by broken lines.

may impair cardiac function further, sometimes causing a vicious circle. Nephrotic Syndrome and Other Hypoalbuminemic States The primary alteration in this disorder is a diminished colloid oncotic pressure due to losses of large quantities of protein into the urine. With severe hypoalbuminemia and the consequent reduced colloid osmotic pressure, the NaCl and H2O that are retained cannot be restrained within the vascular compartment, and total and effective arterial blood volumes decline. This process initiates the edema-forming sequence of events described above, including activation of the RAA system. Impaired renal function contributes further to the formation of edema. A similar sequence of events occurs in other conditions

Edema

Renal vasoconstriction

56 that lead to severe hypoalbuminemia, including (1) severe nutritional deficiency states; (2) severe, chronic liver disease (see later); and (3) protein-losing enteropathy. Cirrhosis

SECTION II Diagnosis of Cardiovascular Disorders

This condition is characterized by hepatic venous outflow blockade, which, in turn, expands the splanchnic blood volume and increases hepatic lymph formation. Intrahepatic hypertension acts as a potent stimulus for renal Na+ retention and a reduction of effective arterial blood volume. These alterations are frequently complicated by hypoalbuminemia secondary to reduced hepatic synthesis, as well as systemic vasodilation, which reduce the effective arterial blood volume further, leading to activation of the RAA system, of renal sympathetic nerves, and of other NaCl- and H2O-retaining mechanisms. The concentration of circulating aldosterone is often elevated by the liver’s failure to metabolize this hormone. Initially, the excess interstitial fluid is localized preferentially proximal (upstream) to the congested portal venous system and obstructed hepatic lymphatics, i.e., in the peritoneal cavity (ascites). In later stages, particularly when there is severe hypoalbuminemia, peripheral edema may develop. The excess production of prostaglandins (PGE2 and PGI2) in cirrhosis attenuates renal Na+ retention. When the synthesis of these substances is inhibited by nonsteroidal anti-inflammatory drugs (NSAIDs), renal function deteriorates and Na+ retention increases. Drug-Induced Edema A large number of widely used drugs can cause edema (Table 7-1). Mechanisms include renal vasoconstriction (NSAIDs and cyclosporine), arteriolar dilatation (vasodilators), augmented renal Na+ reabsorption (steroid hormones), and capillary damage (interleukin 2).

TABLE 7-1 DRUGS ASSOCIATED WITH EDEMA FORMATION Nonsteroidal anti-inflammatory drugs Antihypertensive agents Direct arterial/arteriolar vasodilators Hydralazine Clonidine Methyldopa Guanethidine Minoxidil Calcium channel antagonists α-Adrenergic antagonists Thiazolidinediones Steroid hormones Glucocorticoids Anabolic steroids Estrogens Progestins Cyclosporine Growth hormone Immunotherapies Interleukin 2 OKT3 monoclonal antibody Source: From Chertow.

that in these patients chronic diuretic administration leads to mild blood volume depletion, which causes chronic hyperreninemia and juxtaglomerular hyperplasia. Saltretaining mechanisms appear to overcompensate for the direct effects of the diuretics. Acute withdrawal of diuretics can then leave the Na+-retaining forces unopposed, leading to fluid retention and edema. Decreased dopaminergic activity and reduced urinary kallikrein and kinin excretion have been reported in this condition and may also be of pathogenetic importance.

Idiopathic Edema This syndrome, which occurs almost exclusively in women, is characterized by periodic episodes of edema (unrelated to the menstrual cycle), frequently accompanied by abdominal distention. Diurnal alterations in weight occur with orthostatic retention of NaCl and H2O, so that the patient may weigh several pounds more after having been in the upright posture for several hours. Such large diurnal weight changes suggest an increase in capillary permeability that appears to fluctuate in severity and to be aggravated by hot weather. There is some evidence that a reduction in plasma volume occurs in this condition with secondary activation of the RAA system and impaired suppression of AVP release. Idiopathic edema should be distinguished from cyclical or premenstrual edema, in which the NaCl and H2O retention may be secondary to excessive estrogen stimulation.There are also some cases in which the edema appears to be diuretic-induced. It has been postulated

Treatment: IDIOPATHIC EDEMA

The treatment of idiopathic cyclic edema includes a reduction in NaCl intake, rest in the supine position for several hours each day, and the wearing of elastic stockings (which should be put on before arising in the morning). A variety of pharmacologic agents, including angiotensin-converting enzyme inhibitors, progesterone, the dopamine receptor agonist bromocriptine, and the sympathomimetic amine dextroamphetamine, have all been reported to be useful when administered to patients who do not respond to simpler measures. Diuretics may be helpful initially but may lose their effectiveness with continuous administration; accordingly, they should be employed sparingly, if at all. Discontinuation of diuretics paradoxically leads to diuresis in diureticinduced edema, described above.

disorders. Consequently, the differential diagnosis of gen- 57 eralized edema should be directed toward identifying or excluding these several conditions.

DIFFERENTIAL DIAGNOSIS LOCALIZED EDEMA

GENERALIZED EDEMA

(See also Chap. 17) The presence of heart disease, as manifested by cardiac enlargement and a gallop rhythm, together with evidence of cardiac failure, such as dyspnea, basilar rales, venous distention, and hepatomegaly, usually indicate that edema results from heart failure. Noninvasive tests, such as echocardiography, may be helpful in establishing the diagnosis of heart disease.The edema of heart failure typically occurs in the dependent portions of the body. Edema of the Nephrotic Syndrome Marked proteinuria (>3.5 g/d), hypoalbuminemia (95%) cardiac catheterizations are performed by the percutaneous femoral technique that begins with needle puncture of the common femoral artery or (for right heart catheterization) the femoral vein. A flexible guidewire is inserted through this needle and supports insertion of a vascular access sheath, through which the desired catheters can be advanced.This percutaneous technique can be adapted to other arterial sites such as (1) the brachial and radial artery in patients with peripheral vascular disease involving the abdominal aorta and iliac or femoral arteries or in whom immediate postprocedure ambulation is desired, or (2) the internal jugular vein for right heart catheterization in patients who may require prolonged hemodynamic monitoring. Cardiac catheterization may include a variety of different measurements of pressure and flow (hemodynamics) as well as a variety of different contrast injections recorded as x-ray movies (angiography), determined by the nature of the clinical problem being evaluated, and the extent of information available from prior noninvasive evaluation of left ventricular and valvular function. Full left and right heart hemodynamic studies are generally reserved for patients in whom the noninvasive data are unclear, or in whom intra- and postprocedural hemodynamic monitoring of unstable circulatory status may be desired.

CHAPTER 13 Diagnostic Cardiac Catheterization and Angiography

[percutaneous coronary intervention (PCI); Chap. 36] that can provide definitive correction. Alternatively, diagnostic catheterization may demonstrate only less critical lesions that can be managed medically or severe lesions poorly suited to PCI that may be referred for treatment by cardiac surgery (e.g., coronary bypass surgery, valve replacement, or valve repair). While cardiac catheterization was once considered mandatory in all patients being considered for cardiac surgery, currently many patients with congenital or valvular heart disease undergo surgical correction based solely on clinical and noninvasive test data [e.g., echocardiography and MRI (Chap. 12)], with diagnostic coronary angiography performed in older patients or those with risk factors for or non-invasive testing suggesting coronary disease, prior to surgery. When there is a clinical “need to know,” there are very few absolute contraindications to diagnostic cardiac catheterization in a patient who understands and accepts the associated risks. The risk of death from elective cardiac catheterization approaches 1 in 10,000 (0.01%), but the procedure does carry a small (∼1 in 1000) risk of stroke or myocardial infarction, transient tachy- or bradyarrhythmias, or bruising or bleeding at the catheter insertion site.These complications respond to drug therapy, countershock, or vascular surgical repair, without long-term sequelae. About 1% of patients used to experience allergic reactions to iodinated contrast agents, ranging from urticaria to frank anaphylaxis in sensitive patients, but these have become rare events with current nonionic low-osmolar contrast agents. Other patients (particularly those with baseline renal dysfunction or proteinuria) may develop transient deterioration in renal function, the chance of which may be further reduced by adequate prehydration (50% normal saline, or D5W with 154 meq/L of sodium bicarbonate added, given at 3 mL/kg for 1 h prior to and 1 mL/kg for 6 h following the procedure, absent congestive heart failure), preprocedure administration of N-acetylcysteine (Mucomist, 600 mg orally before and twice a day after the procedure), or the use of an iso-osmolar contrast agent (iodixanol). Newer low- or iso-osmolar contrast agents also reduce the chance of myocardial depression and other side effects (hypotension, nausea, bradycardia, or a sensation of marked warmth following injection) that were once common when earlier high-osmolar contrast agents were used. Cardiac catheterization is generally performed with the patient fasting for the previous 6 h and awake but lightly sedated. The desired level of sedation may be achieved with preprocedure sedatives such as oral diazepam (Valium, 5–10 mg), or with IV conscious sedation using midazolam (Versed, 1 mg) or fentanyl (25–50 µg) following guidelines for conscious sedation. Most elective procedures are performed on an outpatient basis, with the patient discharged with instructions regarding maintenance of a

Right Heart Catheterization This procedure involves measurement of the pressures in the right side of the heart. It was once a routine component of cardiac catheterization but is now used in 200 beats/min. By contrast, the increased rate of firing of Purkinje cells is more limited, rarely producing ventricular tachyarrhythmias >120 beats/min. Normal automaticity may be affected by a number of other factors associated with heart disease. Hypokalemia and ischemia may reduce the activity of the Na+,K+ATPase, thereby reducing the background repolarizing current and enhancing phase 4 diastolic depolarization. The end result would be an increase in the spontaneous firing rate of pacemaking cells. Modest increases in extracellular potassium may render the maximum diastolic potential more positive, thereby also increasing the firing rate of pacemaking cells. A more significant increase in [K+]o, however, renders the heart inexcitable by depolarizing the membrane potential. Normal or enhanced automaticity of subsidiary latent pacemakers produces escape rhythms in the setting of

Principles of Electrophysiology

Note: DAD, delayed afterdepolarization; VT, ventricular tachyarrhythmia; IVR, idioventricular rhythm; EAD, early afterdepolarization; VF, ventricular fibrillation; AV, atrioventricular; HF, heart failure; AP, action potential.

CHAPTER 14

Multicellular

126 failure of more dominant pacemakers. Suppression of a

Heart Rhythm Disturbances

Afterdepolarizations and Triggered Automaticity Triggered automaticity or activity refers to impulse initiation that is dependent on afterdepolarizations (Fig. 14-3). Afterdepolarizations are membrane voltage oscillations that occur during [early afterdepolarizations (EADs)] or following [delayed afterdepolarizations (DADs)] an action potential. The cellular feature common to the induction of DADs is the presence of increased Ca2+ load in the cytosol and

0 mV

EAD

Reactivation of L-type Ca current 50 mV

SECTION III

pacemaker cell by a faster rhythm leads to an increased intracellular Na+ load ([Na+]i), and extrusion of Na+ from the cell by the Na+,K+-ATPase produces an increased background repolarizing current that slows phase 4 diastolic depolarization.At slower rates, the [Na+]i is decreased, as is the activity of the Na+,K+-ATPase, resulting in progressively more rapid diastolic depolarization and warmup of the tachycardia rate. Overdrive suppression and warm-up are characteristic of, but may not be observed in, all automatic tachycardias. Abnormal conduction into tissue with enhanced automaticity (entrance block) may blunt or eliminate the phenomena of overdrive suppression and warm-up of automatic tissue. Abnormal automaticity may underlie atrial tachycardia, accelerated idioventricular rhythms, and ventricular tachycardia, particularly that associated with ischemia and reperfusion. It has also been suggested that injury currents at the borders of ischemic myocardium may depolarize adjacent non-ischemic tissue, predisposing to automatic ventricular tachycardia.

DAD

Intracellular Ca2+ overload 0.5 s

FIGURE 14-3 Schematic action potentials with early (EAD) and delayed afterdepolarizations (DAD). Afterdepolarizations are spontaneous depolarizations in cardiac myocytes. EADs occur before the end of the action potential (phases 2 and 3), interrupting repolarization. DADs occur during phase 4 of the action potential after completion of repolarization. The cellular mechanisms of EADs and DADs differ (see text).

sarcoplasmic reticulum. Inhibition of the Na+,K+-ATPase by digitalis glycosides facilitates, but is not necessary for creating, the Ca2+ overload that predisposes to DADs. Catecholamines and ischemia sufficiently enhance Ca2+ loading to produce DADs. Accumulation of lysophospholipids in ischemic myocardium with consequent Na+ and Ca2+ overload has been suggested as a mechanism for DADs and triggered automaticity. Cells from damaged areas or surviving a myocardial infarction may display spontaneous release of calcium from the sarcoplasmic reticulum, and this may generate “waves” of intracellular calcium elevation and arrhythmias. EADs occur during the action potential and interrupt the orderly repolarization of the myocyte. It has been traditionally held that, unlike DADs, EADs do not depend on a rise in intracellular Ca2+, and that, instead, action potential prolongation and reactivation of depolarizing currents are fundamental to their production. More recent experimental evidence suggests a previously unappreciated interrelationship between intracellular calcium loading and EADs. Cytosolic calcium may increase when action potentials are prolonged.This, in turn, appears to enhance L-type Ca current, further prolonging action potential duration as well as providing the inward current driving EADs. Intracellular calcium loading by action potential prolongation may also enhance the likelihood of DADs. The interrelationship among intracellular [Ca2+], EADs, and DADs may be one explanation for the susceptibility of hearts that are calcium loaded (e.g., in ischemia or congestive heart failure) to develop arrhythmias, particularly on exposure to action potential–prolonging drugs. EAD-triggered arrhythmias exhibit rate dependence. In general, the amplitude of an EAD is augmented at slow rates when action potentials are longer. Rapid pacing will shorten the action potential duration and reduce EAD amplitude, likely due to augmentation of delayed rectifier K+ currents and, perhaps, hastening of Ca2+induced inactivation of L-type Ca currents. Similarly, catecholamines increase heart rate and decrease action potential duration and EAD amplitude, despite the welldescribed effect of β-adrenergic stimulation on increasing L-type Ca current. A fundamental condition that underlies the development of EADs is action potential and QT prolongation. Hypokalemia, hypomagnesemia, bradycardia, and, most commonly, drugs can predispose to the generation of EADs, invariably in the context of prolonging the action potential. Antiarrhythmics with class IA and III action (see later) produce action potential and QT prolongation intended to be therapeutic, but frequently causing arrhythmias. Noncardiac drugs, such as phenothiazines, nonsedating antihistamines, and some antibiotics can also prolong the action potential duration and predispose to EAD-mediated triggered arrhythmias. Decreased [K+]o may paradoxically decrease membrane potassium currents (particularly IKr) in the ventricular

myocyte, explaining why hypokalemia causes action potential prolongation and EADs. In fact, potassium infusions in patients with the congenital long QT syndrome (LQTS) and in those with drug-induced acquired QT prolongation shorten the QT interval. EAD-mediated triggered activity likely underlies initiation of the characteristic polymorphic ventricular tachycardia, torsade de pointes, seen in patients with congenital and acquired forms of the LQTS. Structural heart disease, such as cardiac hypertrophy and failure, may also delay ventricular repolarization (so-called electrical remodeling) and predispose to arrhythmias related to abnormalities of repolarization. The abnormalities of repolarization in hypertrophy and failure are often magnified by concomitant drug therapy or electrolyte disturbances.

slow

block

A Reentrant circuit

gap

B

C

Initiation of reentry

Sustained reentry

D Termination of reentry

FIGURE 14-4 Schematic diagram of reentry. A. The circuit comprises two limbs, one with slow conduction. B. A premature impulse blocks in the fast pathway and conducts over the slow pathway, allowing the fast pathway to recover so that the activation wave can reenter the fast pathway from the retrograde direction. C. During sustained reentry utilizing such a circuit, a gap (excitable gap) exists between the activating head of the wave and the recovering tail. D. One mechanism of termination of reentry is when the conduction and recovery characteristics of the circuit change, and the activating head of the wave collides with the tail, extinguishing the tachycardia.

Principles of Electrophysiology

The most common arrhythmia mechanism is reentry. Reentry is a property of networks of myocytes. Fundamentally, reentry is defined as circulation of an activation wave around an inexcitable obstacle. Thus, the requirements for reentry are two electrophysiologically dissimilar pathways for impulse propagation around an inexcitable region such that unidirectional block occurs in one of the pathways and a region of excitable tissue exists at the head of the propagating wavefront (Fig. 14-4). Structural and electrophysiologic properties of the heart may contribute to the development of the inexcitable obstacle and of

CHAPTER 14

Abnormal Impulse Conduction: Reentry

unidirectional block. The complex geometry of muscle 127 bundles in the heart and spatial heterogeneity of cellular coupling or other active membrane properties (i.e., ionic currents) appear to be critical. A key feature in classifying reentrant arrhythmias, particularly for therapy, is the presence and size of an excitable gap. An excitable gap exists when the tachycardia circuit is longer than the tachycardia wavelength (λ = conduction velocity × refractory period, representing the size of the circuit that can sustain reentry), allowing appropriately timed stimuli to reset propagation in the circuit. Reentrant arrhythmias may exist in the heart in the absence of an excitable gap and with a tachycardia wavelength nearly the same size as the path length. In this case, the wavefront propagates through partially refractory tissue with no anatomic obstacle and no fully excitable gap; this is referred to as leading circle reentry, a form of functional reentry (reentry that depends on functional properties of the tissue). Unlike excitable gap reentry, there is no fixed anatomic circuit in leading circle reentry, and it may therefore not be possible to disrupt the tachycardia with pacing or destruction of a part of the circuit. Furthermore, the circuit in leading circle reentry tends to be less stable than that in excitable gap reentrant arrhythmias, with large variations in cycle length and predilection to termination. Anatomically determined, excitable gap reentry can explain several clinically important tachycardias, such as AV reentry, atrial flutter, bundle branch reentry ventricular tachycardia, and ventricular tachycardia in scarred myocardium. Atrial flutter represents an example of a reentrant tachycardia with a large excitable gap not always due to an anatomic constraint but to functional block (reflecting the special properties of the crista terminalis discussed above). There is strong evidence to suggest that arrhythmias, such as atrial and ventricular fibrillation, are associated with more complex activation of the heart and are due to functional reentry. Structural heart disease is associated with changes in conduction and refractoriness that increase the risk of reentrant arrhythmias. Chronically ischemic myocardium exhibits a down-regulation of the gap junction channel protein (connexin 43) that carries intercellular ionic current. The border zones of infarcted and failing ventricular myocardium exhibit not only functional alterations of ionic currents but also remodeling of tissue and altered distribution of gap junctions.The changes in gap junction channel expression and distribution, in combination with macroscopic tissue alterations, support a role for slowed conduction in reentrant arrhythmias that complicate chronic coronary artery disease. Aged human atrial myocardium exhibits altered conduction, manifest as highly fractionated atrial electrograms, producing an ideal substrate for the reentry that may underlie the very common development of atrial fibrillation in the elderly.

128

Approach to the Patient: CARDIAC ARRHYTHMIA

SECTION III Heart Rhythm Disturbances

The evaluation of patients with suspected cardiac arrhythmias is highly individualized; however, two key features, the history and ECG, are pivotal in directing the diagnostic workup and therapy. Patients with cardiac arrhythmias exhibit a wide spectrum of clinical presentations from asymptomatic ECG abnormalities to survival from cardiac arrest. In general, the more severe the presenting symptoms, the more aggressive are the evaluation and treatment. Loss of consciousness that is believed to be of cardiac origin typically mandates an exhaustive search for the etiology and often requires invasive, device-based therapy.The presence of structural heart disease and prior myocardial infarction dictates a change in the approach to the management of syncope or ventricular arrhythmias.The presence of a family history of serious ventricular arrhythmias or premature sudden death will influence the evaluation of presumed heritable arrhythmias. The physical examination is focused on determining if there is cardiopulmonary disease that is associated with specific cardiac arrhythmias. The absence of significant cardiopulmonary disease often, but not always, suggests benignity of the rhythm disturbance. In contrast, palpitations, syncope, or near syncope in the setting of significant heart or lung disease has more ominous implications. In addition, the physical examination may reveal the presence of a persistent arrhythmia such as atrial fibrillation. The judicious use of noninvasive diagnostic tests is an important element in the evaluation of patients with arrhythmias, and there is none more important that the ECG, particularly if recorded at the time of symptoms. Uncommon but diagnostically important signatures of electrophysiologic disturbances may be unearthed on the resting ECG, such as delta waves in Wolff-Parkinson-White (WPW) syndrome, prolongation or shortening of the QT interval, right precordial ST-segment abnormalities in Brugada syndrome, and epsilon waves in arrhythmogenic right ventricular dysplasia.Variants of body surface ECG recording can provide important information about arrhythmia substrates and triggers. Holter monitoring and event recording, either continuous or intermittent, record the body surface ECG over longer periods of time, enhancing the possibility of observing the cardiac rhythm during symptoms. Implantable long-term monitors and commercial ambulatory ECG monitoring services exist that permit prolonged telemetric monitoring for both diagnosis and to assess the efficacy of therapy. Long-term recordings permit the assessment of the time-varying behavior of the heart rhythm. Heart rate variability (HRV) and QT interval variability (QTV)

provide noninvasive methods to assess autonomic nervous system influence on the heart. HRV arises because of subtle changes in sinus rate due to changes in sympathovagal input to the sinus node. Normal time domain, frequency domain, and geometric methods metrics have been established for HRV; a decrease in HRV and an increase in low-frequency power have been associated with increased sympathetic nervous system tone and increased mortality in patients after myocardial infarction. Signal-averaged electrocardiography (SAECG) uses signal-averaging techniques to amplify small potentials in the body surface ECG that are associated with slow conduction in the myocardium. The presence of these small potentials, referred to as late potentials because of their timing with respect to the QRS complex, and prolongation of the filtered (or averaged) QRS duration are indicative of slowed conduction in the ventricle and have been associated with an increased risk of ventricular arrhythmias after myocardial infarction. Exercise electrocardiography is important in determining the presence of myocardial demand ischemia; more recently, analysis of the morphology of the QT interval with exercise has been used to assess the risk of serious ventricular arrhythmias. Microscopic alterations in the T wave [T wave alternans (TWA)] at low heart rates identify patients at risk for ventricular arrhythmias. A number of other tests of the variability in the T-wave morphology or duration of the QT interval have been used to assess instability in repolarization of the ventricle and an increased risk of arrhythmias. Head-up tilt (HUT) testing is a useful in the evaluation of some patients with syncope. The physiologic response to HUT is incompletely understood; however, redistribution of blood volume and increased ventricular contractility occur consistently. Exaggerated activation of a central reflex in response to HUT produces a stereotypic response of an initial increase in heart rate, then a drop in blood pressure followed by a reduction in heart rate characteristic of neurally mediated hypotension. Other responses to HUT may be observed in patients with orthostatic hypotension and autonomic insufficiency. HUT is most often used in patients with recurrent syncope, although it may be useful in patients with single syncopal episodes with associated injury, particularly in the absence of structural heart disease. In patients with structural heart disease, HUT may be indicated in those with syncope, in whom other causes (e.g., asystole, ventricular tachyarrhythmias) have been excluded. HUT has been suggested as a useful tool in the diagnosis and therapy of recurrent idiopathic vertigo, chronic fatigue syndrome, recurrent transient ischemic attacks, and repeated falls of unknown etiology in the elderly. Importantly, HUT is relatively contraindicated in the

ANTIARRHYTHMIC DRUG THERAPY The inter-

action of antiarrhythmic drugs with cardiac tissues and the resulting electrophysiologic changes are complex. An incomplete understanding of the effects of these drugs has produced serious missteps that have had adverse effects on patient outcomes and the development of newer pharmacologic agents. Currently, antiarrhythmic drugs have been relegated to an ancillary role in the treatment of most cardiac arrhythmias. There are several explanations for the complexity of antiarrhythmic drug action: the structural similarity of target ion channels; regional differences in the levels of expression of channels and transporters, which change with disease; time and voltage dependence of drug action; and the effect of these drugs on targets other than ion channels. Recognizing the limitations of any scheme to classify antiarrhythmic agents, a shorthand that is useful in describing the major mechanisms of action is of some utility. Such a classification scheme was proposed in 1970 by Vaughan-Williams and later modified by Singh and Harrison. The classes of antiarrhythmic action are: class I; local anesthetic effect due to blockade of Na+ current; class II, interference with the action of catecholamines at the β-adrenergic receptor; class III, delay of repolarization due to inhibition of K+ current or activation of depolarizing current; class IV, interference with calcium conductance (Table 14-2). The limitations of the Vaughan-Williams classification

129

ANTIARRHYTHMIC DRUG ACTIONS CLASS ACTIONS DRUG

I

Quinidine

++

++

Procainamide

++

++

Flecainide Propafenone Sotalol Dofetilide Amiodarone

+++ ++

Ibutilide

++

II

+ ++ ++

III

IV

MISCELLANEOUS ACTION

α-Adrenergic blockade Ganglionic blockade

+ +++ +++ +++ +++

+

α-Adrenergic blockade Na+ channel activator

scheme include multiple actions of most drugs, overwhelming consideration of antagonism as a mechanism of action, and the fact that several agents have none of the four classes of action in the scheme. CATHETER ABLATION The use of catheter ablation is based on the principle that there is a critical anatomic region of impulse generation or propagation required for the initiation and maintenance of cardiac arrhythmias. Destruction of such a critical region results in the elimination of the arrhythmia. The use of radiofrequency (RF) energy in clinical medicine is nearly a century old. The first catheter ablation using a DC energy source was performed in the early 1980s by Scheinman and colleagues. By the early 1990s, RF had been adapted for use in catheter-based ablation in the heart (Fig. 14-5). The RF frequency band (300–30,000 kHz) is used to generate energy for several biomedical applications, including coagulation and cauterizing tissues. Energy of this frequency will not stimulate skeletal muscle or the heart and heats tissue by a resistive mechanism, with the intensity of heating being proportional to the delivered power. The density of power in the tissue falls off rapidly (with the 4th power of the radius or distance), as does the temperature, allowing for the production of smallvolume lesions. The applied power, energy, or current are not good predictors of lesion size; temperature at the electrode-tissue interface is the best predictor, with temperatures >55°C consistently producing tissue necrosis. The temperature rise at the tissue-electrode interface is rapid, but heating is slower in the tissue, and steady-state lesion size may be not achieved for ≥40 s of radiofrequency energy application. Notably, tissue temperature may remain high for many seconds despite cessation of energy delivery, producing undesired ablation of cardiac structures. Alternative, less frequently used energy sources for catheter ablation of cardiac arrhythmias

Principles of Electrophysiology

Treatment: CARDIAC ARRHYTHMIAS

TABLE 14-2

CHAPTER 14

presence of severe coronary artery disease with proximal coronary stenoses, known severe cerebrovascular disease, severe mitral stenosis, and obstruction to left ventricular outflow (e.g., aortic stenosis).The method of HUT is variable, but the angle of tilt and the duration of upright posture are central to the diagnostic utility of the test.The use of pharmacologic provocation of orthostatic stress with isoproterenol, nitrates, adenosine, and edrophonium have been used to shorten the test and enhance specificity. Electrophysiologic testing is central to the understanding and treatment of many cardiac arrhythmias. Indeed, most frequently electrophysiologic testing is interventional, providing both diagnosis and therapy. The components of the electrophysiologic test are baseline measurements of conduction under resting and stressed (rate or pharmacologic) conditions and maneuvers, both pacing and pharmacologic, to induce arrhythmias. A number of sophisticated electrical mapping and catheter-guidance techniques have been developed to facilitate catheter-based therapeutics in the electrophysiology laboratory.

130

A

SECTION III Heart Rhythm Disturbances

FIGURE 14-5 Catheter ablation of cardiac arrhythmias. A. A schematic of the lead system and generator in a patient undergoing radiofrequency catheter ablation (RFA); the circuit involves the lead in the heart and a dispersive patch placed on the body surface (usually the back). The inset shows a diagram of the heart with a catheter located at the AV valve ring for ablation of an accessory pathway. B. A right anterior oblique fluoroscopic image of the catheter position for ablation of a left-sided accessory pathway. A catheter is placed in the atrial side of the mitral valve ring (abl) via a transseptal puncture; other catheters are placed in the coronary sinus (CS) to

include microwaves (915 MHz or 2450 MHz), lasers, ultrasound, or freezing (cryoablation). In addition to RF energy, cryoablation is being used clinically and is a safe and effective alternative to RF, especially with ablation in the region of the AV node. At temperatures just below 32°C, membrane ion transport is disrupted, producing depolarization of cells, decreased action potential amplitude and duration, and slowed conduction velocity (resulting in local conduction block)—all of which are reversible, if the tissue is rewarmed in a

record intracardiac electrograms around the mitral annulus; a circumferential catheter in the right atrium (RA) and a catheter in the right ventricular apex (RV). C. Body surface ECG recordings (I, II, V1) and endocardial electrograms (HRA: high right atrium; HISp: proximal His-bundle electrogram; CS 7,8 recordings from poles 7 and 8 of a decapolar catheter placed in the coronary sinus) during RFA of a leftsided accessory pathway in a patient with WPW syndrome. The QRS narrows at the fourth complex, the arrow shows the His-bundle electrogram, which becomes apparent with elimination of ventricular preexcitation over the accessory pathway.

timely fashion. Tissue cooling can be used for mapping and ablation. Cryomapping can be used to confirm the location of a desired ablation target, such as an accessory pathway in WPW syndrome, or can be used to determine the safety of ablation around the AV node by monitoring AV conduction during cooling. Another advantage of cryoablation is that once the catheter tip cools below freezing, it adheres to the tissue, increasing catheter stability independent of the rhythm or pacing.

FURTHER READINGS AKAR FG, TOMASELLI GF: Genetic basis of cardiac arrhythmias, in Hurst’s The Heart, 11th ed, V Fuster et al (eds). New York, McGraw-Hill, 2004 ———: Genetic basis of cardiac arrhythmias, in Hurst’s The Heart, 12th ed,V Fuster et al (eds). New York, McGraw-Hill, 2007 HILLE B: Ion Channels of Excitable Membranes, 3d ed. Sunderland, MA, Sinauer Associates, Inc, 2001, Chaps 1, 3, 4, 21, 22

JOSEPHSON ME: Clinical Cardiac Electrophysiology:Techniques and Interpretations, 3d ed. Philadelphia, Lippincott Williams & Wilkins, 2002 ———: Clinical Cardiac Electrophysiology: Techniques and Interpretations, 4th ed. Philadelphia, Lippincott Williams & Wilkins, 2008 SAKSENA S, CAMM AJ (eds): Electrophysiological Disorders of the Heart. Philadelphia, Elsevier Churchill Livingstone, 2005 ZIPES DP, JALIFE J (eds): Cardiac Electrophysiology: From Cell to Bedside, 4th ed. Philadelphia, Elsevier, 2004 ——— (eds): Cardiac Electrophysiology: From Cell to Bedside, 5th ed. Philadelphia, Elsevier, 2009

131

CHAPTER 14 Principles of Electrophysiology

CHAPTER 15

THE BRADYARRHYTHMIAS Gordon F. Tomaselli

SA Node Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Atrioventricular Conduction Disease . . . . . . . . . . . . . . . . . . . 137 Permanent Pacemakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146

Electrical activation of the heart normally originates in the sinoatrial (SA) node, the predominant pacemaker. Other subsidiary pacemakers in the atrioventricular (AV) node, specialized conducting system, and muscle may initiate electrical activation if the SA node is dysfunctional or suppressed. Typically subsidiary pacemakers discharge at a slower rate and, in the absence of an appropriate increase in stroke volume, may result in tissue hypoperfusion. Spontaneous activation and contraction of the heart are the consequence of the specialized pacemaking tissue found within these anatomic locales. As described in Chap. 14, action potentials in the heart are regionally heterogeneous. The action potentials in cells isolated from nodal tissue are distinct from those recorded from atrial and ventricular myocytes (Fig. 15-1). The complement of ionic currents present in nodal cells results in a less negative resting membrane potential compared with atrial or ventricular myocytes. Electrical diastole in nodal cells is characterized by slow diastolic depolarization (phase 4), which generates an action potential as the membrane voltage reaches threshold. The action potential upstrokes (phase 0) are slow compared with atrial or ventricular myocytes, being mediated by calcium rather than sodium current. Cells with properties of SA and AV nodal tissue are electrically connected to the remainder of the myocardium by cells with an electrophysiologic phenotype between that of nodal cells and atrial or ventricular myocytes. Cells in the SA node exhibit the most rapid phase 4 depolarization and thus are the dominant pacemakers in the normal heart. Bradycardia results from either a failure of impulse initiation or impulse conduction. Failure of impulse initiation

may be caused by depressed automaticity resulting from a slowing or failure of phase 4 diastolic depolarization (Fig. 15-2), which may result from disease or exposure to drugs. Prominently, the autonomic nervous system modulates the rate of phase 4 diastolic depolarization and, thus, the firing rate of both primary (SA node) and subsidiary pacemakers. Failure of conduction of an impulse from nodal tissue to atrial or ventricular myocardium may produce bradycardia as a result of exit block. Conditions that alter activation and connectivity of cells (e.g., fibrosis) in the heart may result in failure of impulse conduction. SA node dysfunction and AV conduction block are the most common causes of pathologic bradycardia. SA node dysfunction may be difficult to distinguish from physiologic sinus bradycardia, particularly in the young. SA node dysfunction increases in frequency between the fifth and sixth decades of life and should be considered in patients with fatigue, exercise intolerance, or syncope and sinus bradycardia. Transient AV block is common in the young and likely the result of the high vagal tone found in up to 10% of young adults. Acquired and persistent failure of AV conduction is decidedly rare in healthy adult populations, with an estimated incidence of ∼200/million population per year. Permanent pacemaking is the only reliable therapy for symptomatic bradycardia in the absence of extrinsic and reversible etiologies such as increased vagal tone, hypoxia, hypothermia, and drugs (Table 15-1). Approximately 50% of the 150,000 permanent pacemakers implanted in the United States and 20–30% of the 150,000 of those implanted in Europe were implanted for SA node disease.

132

Voltage, mV

120

−100

133

ECa + 120 mV ENa + 70 mV

1 2

0 mV ECI −30 mV

0

0 3 4

EK −90 mV

Ventricular

FIGURE 15-1 Action potential profiles recorded in cells isolated from SA or AV nodal tissue compared to that of cells from atrial or ventricular myocardium. Nodal cell action potentials exhibit

Acetylcholine

Control 0 mV

–50 mV

ΙCa-T, Ι F,

Repolarizing currents

ΙK, Ι K1, Ι K ACh

ΙCa-L

FIGURE 15-2 Schematics of nodal action potentials and the currents that contribute to phase 4 depolarization. Relative increases in depolarizing L- (ICa-L) and T- (ICa-T) type calcium and pacemaker currents (If) along with a reduction in repolarizing inward rectifier (IK1) and delayed rectifier (IK) potassium currents result in depolarization. Activation of ACh-gated (IKACh) potassium current and beta blockade slows the rate of phase 4 and decreases the pacing rate. (Modified from J Jalife et al: Basic Cardiac Electrophysiology for the Clinician, Blackwell Publishing, 1999.)

SA NODE DISEASE Structure and Physiology of the SA Node The SA node is composed of a cluster of small fusiform cells located in the sulcus terminalis on the epicardial surface of the heart at the right atrial–superior vena caval junction, where they envelop the SA nodal artery. The SA node is structurally heterogeneous, but the central prototypic nodal cells have fewer distinct myofibrils than the surrounding atrial myocardium, no intercalated disks visible on light microscopy, a poorly developed sarcoplasmic reticulum, and no T-tubules. Cells in the peripheral regions of the SA node are transitional in both structure and function. The SA nodal artery arises from the right coronary artery in 55–60% and left circumflex artery in 40–45% of persons. The SA node is richly innervated by sympathetic and parasympathetic nerves and ganglia.

200 ms

more depolarized resting membrane potentials, slower phase 0 upstrokes, and phase 4 diastolic depolarization.

Irregular and slow propagation of impulses from the SA node can be explained by the electrophysiology of nodal cells and the structure of the SA node itself. The action potentials of SA nodal cells are characterized by a relatively depolarized membrane potential (Fig. 15-1) of −40 to −60 mV, slow phase 0 upstroke, and relatively rapid phase 4 diastolic depolarization compared to the action potentials recorded in cardiac muscle cells. The relative absence of inward rectifier potassium current (IK1) accounts for the depolarized membrane potential; the slow upstroke of phase 0 is the result of the absence of available fast sodium current (INa) and is mediated by L-type calcium current (ICa-L); and phase 4 depolarization is the result of the aggregate activity of a number of ionic currents. Prominently, both L- and T-type (ICa-T) calcium currents, the pacemaker current (so-called funny current, or If) formed by the tetramerization of hyperpolarization-activated cyclic nucleotide-gated channels, and the electrogenic sodium-calcium exchanger provide depolarizing current that is antagonized by delayed rectifier (IKr) and acetylcholine-gated (IKACh) potassium currents. ICa-L, ICa-T, and If are modulated by β-adrenergic stimulation and IKACh by vagal stimulation, explaining the exquisite sensitivity of diastolic depolarization to autonomic nervous system activity. The slow conduction within the SA node is explained by the absence of INa and poor electrical coupling of cells in the node, resulting from sizeable amounts of interstitial tissue and a low abundance of gap junctions. The poor coupling allows for graded electrophysiological properties within the node, with the peripheral transitional cells being silenced by electrotonic coupling to atrial myocardium. Etiology of SA Nodal Disease SA nodal dysfunction has been classified as intrinsic or extrinsic. The distinction is important because extrinsic dysfunction is often reversible and should generally be corrected before considering pacemaker therapy (Table 15-1). The most common causes of extrinsic SA node dysfunction are drugs and autonomic nervous system

The Bradyarrhythmias

Depolarizing currents

Nodal

CHAPTER 15

Phase 4

Atrial

134

TABLE 15-1 ETIOLOGIES OF SA NODE DYSFUNCTION

SECTION III Heart Rhythm Disturbances

EXTRINSIC

INTRINSIC

Autonomic Carotid sinus hypersensitivity Vasovagal (cardioinhibitory) stimulation Drugs Beta blockers Calcium channel blockers Digoxin Antiarrhythmics (class I and III) Adenosine Clonidine (other sympatholytics) Lithium carbonate Cimetidine Amitriptyline Phenothiazines Narcotics (methadone) Pentamidine Hypothyroidism Sleep apnea Hypoxia Endotracheal suctioning (vagal maneuvers) Hypothermia Increased intracranial pressure

Sick sinus syndrome (SSS) Coronary artery disease (chronic and acute MI) Inflammatory Pericarditis Myocarditis (including viral) Rheumatic heart disease Collagen vascular diseases Lyme disease Senile amyloidosis Congenital heart disease TGA/Mustard and Fontan repairs Iatrogenic Radiation therapy Post surgical Chest trauma Familial AD SSS, OMIM #163800 (15q24-25) AR SSS, OMIM #608567 (3p21) SA node disease with myopia, OMIM 182190 Kearns-Sayre syndrome, OMIM #530000 Myotonic dystrophy Type 1, OMIM #160900 (19q13.2-13.3) Type 2, OMIM #602668 (3q13.3-q24) Friedreich’s ataxia, OMIM #229300 (9q13, 9p23-p11)

Note: MI, myocardial infarction; TGA, transposition of the great arteries; AD, autosomal dominant; AR, autosomal recessive; OMIM, Online Mendelian Inheritance in Man (database).

influences that suppress automaticity and/or compromise conduction. Other extrinsic causes include hypothyroidism, sleep apnea, and conditions likely to occur in critically ill patients such as hypothermia, hypoxia, increased intracranial pressure (Cushing’s response), and endotracheal suctioning via activation of the vagus nerve. Intrinsic sinus node dysfunction is degenerative and often characterized pathologically by fibrous replacement of the SA node or its connections to the atrium. Acute and chronic coronary artery disease (CAD) may be associated with SA node dysfunction, although in the setting of acute myocardial infarction (MI; typically inferior), the abnormalities are transient. Inflammatory processes may alter SA node function, ultimately producing replacement fibrosis. Pericarditis, myocarditis, and rheumatic heart disease have been associated with SA nodal disease with sinus bradycardia, sinus arrest, and exit block. Carditis associated with systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and mixed connective tissue disorders (MCTDs) may also affect SA node structure and function. Senile amyloidosis is an infiltrative disorder in patients typically in their ninth decade of life; deposition of amyloid protein in the atrial myocardium can impair SA node function. Some SA node disease is iatrogenic and the result of surgical correction

of congenital heart disease, particularly palliative repair of corrected transposition of the great arteries by the Mustard procedure. Rare heritable forms of sinus node disease have been described, and several have been genetically characterized. Autosomal dominant sinus node dysfunction in conjunction with supraventricular tachycardia (i.e., tachycardiabradycardia variant of sick-sinus syndrome, SSS) has been linked to mutations in the pacemaker current (If) subunit gene HCN4 on chromosome 15. An autosomal recessive form of SSS with the prominent feature of atrial inexcitability and absence of P waves on the electrocardiogram (ECG) is caused by mutations in the cardiac sodium channel gene, SCN5A, on chromosome 3. SSS associated with myopia has been described but not genetically characterized. There are several neuromuscular diseases including Kearns-Sayre syndrome (ophthalmoplegia, pigmentary degeneration of the retina, and cardiomyopathy) and myotonic dystrophy that have a predilection for the conducting system and SA node. SSS in both the young and the elderly is associated with an increase in fibrous tissue in the SA node. The onset of SSS may be hastened by coexisting disease, such as CAD, diabetes mellitus, hypertension, and valvular diseases and cardiomyopathies.

Clinical Features of SA Node Disease

Electrocardiography of SA Node Disease

II

II

V

V

FIGURE 15-3 Sinus slowing and pauses on the ECG. The ECG is recorded during sleep in a young patient without heart disease. The heart rate before the pause is slow, and the PR interval is prolonged consistent with an increase in vagal tone.

The P waves have a morphology consistent with sinus rhythm. The recording is from a two-lead telemetry system where the tracing labeled II mimics frontal lead II and V represents lead MCL 1 which mimics lead V1 of the standard 12-lead ECG.

The Bradyarrhythmias

The electrocardiographic manifestations of SA node dysfunction include sinus bradycardia, sinus pauses, sinus arrest, sinus exit block, tachycardia (in SSS), and chronotropic incompetence. It is often difficult to distinguish pathologic from physiologic sinus bradycardia. By definition sinus bradycardia is a rhythm driven by the SA node with a rate of 75 years Congestive heart failure Left ventricular dysfunction Marked left atrial enlargement (>5.0 cm) Spontaneous echo contrast

The Tachyarrhythmias

TABLE 16-1

CHAPTER 16

appears to have a well-defined etiology, such as acute hyperthyroidism, an acute vagotonic episode, or acute alcohol intoxication. Acute AF is particularly common during the acute or early recovery phase of major vascular, abdominal, and thoracic surgery where autonomic fluxes and/or direct mechanical irritation potentiate the arrhythmia. AF may also be triggered by other supraventricular tachycardias (p. 160), such as AV nodal reentrant tachycardia (AVNRT), and elimination of these arrhythmias may prevent AF recurrence. AF has clinical importance related to (1) the loss of atrial contractility, (2) the inappropriate fast ventricular response, and (3) the loss of atrial appendage contractility and emptying leading to the risk of clot formation and subsequent thromboembolic events. Symptoms from AF vary dramatically. Many patients are asymptomatic and have no apparent hemodynamic consequences to the development of AF. Other patients experience only minor palpitations or sense irregularity of their pulse. Many patients, however, experience severe palpitations. The hemodynamic effect in patients can be quite dramatic, depending on the need for normal atrial contractility and the ventricular response. Hypotension, pulmonary congestion, and anginal symptoms may be severe in some patients. In patients with the LV diastolic dysfunction that occurs with hypertension, hypertrophic cardiomyopathy, or obstructive aortic valvular disease, symptoms may be even more dramatic, especially if the ventricular rate does not permit adequate ventricular filling. Exercise intolerance and easy fatigability are the hallmarks of poor rate control with exertion. Occasionally, the only manifestation of AF is severe dizziness or syncope associated with the pause that occurs upon termination of AF before sinus rhythm resumes (Fig. 16-1). The ECG in AF is characterized by the lack of organized atrial activity and the irregularly irregular ventricular response. Occasionally, one needs to record from multiple ECG leads simultaneously to identify the chaotic continuous atrial activation. Lead V1 may frequently show the appearance of organized atrial activity that mimics AFL.This occurs because the crista terminalis serves as an effective anatomic barrier to electrical conduction, and the activation of the lateral right atrium may be represented by a more uniform activation wavefront that originates over the roof of the right atrium. ECG assessment of the PP interval (1.8 on at least two separate occasions prior to attempts at cardioversion. Termination of AF acutely may be warranted based on clinical parameters and/or hemodynamic status. Confirmation of appropriate anticoagulation status as described above must be documented unless symptoms and clinical status warrant emergent intervention. Direct current transthoracic cardioversion during shortacting anesthesia is a reliable way to terminate AF. Conversion rates using a 200-J biphasic shock delivered synchronously with the QRS complex typically are >90%. Pharmacologic therapy to terminate AF is less reliable. Oral and/or IV administration of amiodarone or procainamide have only modest success. The acute IV administration of ibutilide appears to be somewhat more effective and may be used in selected patients to facilitate termination with direct current (DC) cardioversion (Tables 16-2 and 16-3). Pharmacologic therapy to maintain sinus rhythm can be instituted once sinus rhythm has been established or in anticipation of cardioversion to attempt to maintain sinus rhythm (Table 16-3). A single episode of AF may not warrant any intervention or only a short course of beta blocker therapy. To prevent recurrent AF

Heart Rhythm Disturbances

unresponsive to beta blockade, a trial of antiarrhythmic therapy may be warranted, particularly if the AF is associated with rapid rates and/or significant symptoms. The selection of antiarrhythmic agents should be dictated primarily by the presence or absence of coronary artery disease, depressed LV function not attributable to a reversible tachycardia-induced cardiomyopathy, and/or severe hypertension with evidence of marked LV hypertrophy. The presence of any significant structural heart disease typically narrows treatment to the use of sotalol, amiodarone, or dofetilide. Severely depressed LV function may preclude sotalol therapy or require only low-dose therapy be considered. Owing to the risk of QT prolongation and polymorphic VT, sotalol and dofetilide need to be initiated in hospital in most cases. In patients without evidence of structural heart disease or hypertensive heart disease without evidence of severe hypertrophy, the use of the class IC antiarrhythmic agents flecainide or propafenone appears to be well tolerated and does not have significant proarrhythmia risk. It is important to recognize that no drug is uniformly effective, and arrhythmia recurrence should be anticipated in over half the patients during long-term follow-up regardless of type and number of agents tried. It is also important to recognize that although the maintenance of sinus rhythm has been associated with improved long-term survival, the survival outcome of patients randomized to the pharmacologic maintenance of sinus rhythm was not superior to those treated

TABLE 16-2 COMMONLY USED ANTIARRHYTHMIC AGENTS—INTRAVENOUS DOSE RANGE/PRIMARY INDICATION DRUG

LOADING

MAINTENANCE

PRIMARY INDICATION

CLASSa

Adenosine

6–18 mg (rapid bolus)

N/A

—

Amiodarone

15 mg/min for 10 min, 1 mg/min for 6 h 0.25 mg q2h until 1.0 mg total 0.25 mg/kg over 3–5 min (max 20 mg) 500 µg/kg over 1 min 1 mg over 10 min if over 60 kg 1–3 mg/kg at 20–50 mg/min 5 mg over 3–5 min times 3 doses 15 mg/kg over 60 min 6–10 mg/kg at 0.3–0.5 mg/kg per min 5–10 mg over 3–5 min

0.5–1 mg/min

Terminate reentrant SVT involving AV node AF, AFL, SVT, VT/VF

0.125–0.25 mg/d 5–15 mg/h

AF/AFL rate control SVT, AF/AFL rate control

— IV

50 µg/kg per min N/A 1–4 mg/min 1.25–5 mg q6h

II III IB II

1–4 mg/min N/A

AF/AFL rate control Terminate AF/AFL VT SVT, AF rate control; exerciseinduced VT; long QT Convert/prevent AF/VT Convert/prevent AF/VT

2.5–10 mg/h

SVT, AF rate control

IV

Digoxin Diltiazem Esmolol Ibutilide Lidocaine Metoprolol Procainamide Quinidine Verapamil a

III

IA IA

Classification of antiarrhythmic drugs: Class I—agents that primarily block inward sodium current; class IA agents also prolong action potential duration; class II—antisympathetic agents; class III—agents that primarily prolong action potential duration; class IV—calcium channel-blocking agents. Note: SVT, supraventricular tachycardia; AV, atrioventricular; AF, atrial fibrillation; AFL, atrial flutter; VT, ventricular tachycardia; VF, ventricular fibrillation.

TABLE 16-3

155

COMMONLY USED ANTIARRHYTHMIC AGENTS—CHRONIC ORAL DOSING/PRIMARY INDICATIONS HALF-LIFE, h

PRIMARY ROUTE(S) OF METABOLISM/ELIMINATION

MOST COMMON INDICATION

Acebutolol

200–400 mg q12h

6–7

Renal/hepatic

Amiodarone Atenolol

100–400 qd 25–100 mg/d

40–55 d 6–9

Hepatic Renal

Digoxin Diltiazem Disopyramide Dofetilide Flecainide Metoprolol

0.125–0.5 qd 30–60 q6h 100–300 q6–8h 0.125–0.5 q12h 50–200 q12h 25–100 q6h

38–48 3–4.5 4–10 10 7–22 3–8

Renal Hepatic Renal 50%/hepatic Renal Hepatic 75%/renal Hepatic

Mexiletine Moricizine Nadolol Procainamide Propafenone Quinidine Sotalol Verapamil

150–300 q8–12h 100–400 q8h 40–240 mg/d 250–500 q3–6h 150–300 q8h 300–600 q6h 80–160 q12h 80–120 q6–8h

10–14 3–13 10–24 3–5 2–8 6–8 12 4.5–12

Hepatic Hepatic 60%/renal Renal Hepatic/renal Hepatic Hepatic 75%/renal Renal Hepatic/renal

AF rate control/SVT Long QT/RVOT VT AF/VT prevention AF rate control/SVT Long QT/RVOT VT AF rate control AF rate control/SVT AF/SVT prevention AF prevention AF/SVT/VT prevention AF rate control/SVT Long QT/RVOT VT VT prevention AF prevention Same as metoprolol AF/SVT/VT prevention AF/SVT/VT prevention AF/SVT/VT prevention AF/VT prevention AF rate control/RVOT VT Idiopathic LV VT

CLASSa

II III II — IV Ia III Ic II Ib Ic II Ia Ic Ia III IV

a

Classification of antiarrhythmic drugs: Class I—agents that primarily block inward sodium current; class II—antisympathetic agents; class III—agents that primarily prolong action potential duration; class IV—calcium channel-blocking agents. Note: AF, atrial fibrillation; SVT, supraventricular tachycardia; RVOT, right ventricular outflow tract; VT, ventricular tachycardia; LV, left ventriclar.

with rate control and anticoagulation in the AFFIRM and RACE trials. The AFFIRM and RACE trials compared outcome with respect to survival and thromboembolic events in patients with AF and risk factors for stroke using the two treatment strategies. It is believed that the poor outcome related to pharmacologic therapy used to maintain sinus rhythm was primarily due to frequent inefficacy of such drug therapy and an increased incidence of asymptomatic AF. Many of the drugs used for rhythm control, including sotalol, amiodarone, propafenone, and flecainide, enhance slowing of AV nodal conduction. The absence of symptoms frequently leads to stopping anticoagulant therapy, and asymptomatic AF without anticoagulation increases stroke risk. Any consideration for stopping anticoagulation must, therefore, be accompanied by a prolonged period of ECG monitoring to document asymptomatic AF. It is also recommended that patients participate in monitoring by learning to take their pulse on a twice-daily basis and to reliably identify its regularity if discontinuing anticoagulant therapy is seriously contemplated. It is clear that to reduce the risk of drug-induced complications when treating AF, a thorough understanding of the drug planned to be used is critical— its dosing, metabolism, and common side effects and important drug-drug interactions. This information has

been summarized in Tables 16-2, 16-3, 16-4, and 16-5 and serves as a starting point for a more complete review. When using antiarrhythmic agents that slow atrial conduction, strong consideration should be given to adding a beta blocker or a calcium channel blocker (verapamil or diltiazem) to the treatment regimen. This should help to avoid a rapid ventricular response if AF is converted to “slow” AF with the drug therapy (Fig. 16-5). This is an option in patients who are asymptomatic or symptomatic due to the resulting tachycardia. Rate control is frequently difficult to achieve in patients who have paroxysmal AF. In patients with more persistent forms of AF, rate control with beta blockers, calcium channel blockers, diltiazem or verapamil, and/or digoxin can frequently be achieved. Using the drugs in combination may avoid some of the common side effects seen with high-dose monotherapy. An effort should be made to document the adequacy of rate control to reduce the risk of a tachycardia-induced cardiomyopathy. Heart rates >80 beats/min at rest or 100 beats/min with very modest physical activity are indications that rate control is inadequate in persistent AF. Extended periods of ECG monitoring and assessment of heart rate with exercise should be considered.

CHRONIC RATE CONTROL

The Tachyarrhythmias

DOSING ORAL, mg, MAINTENANCE

CHAPTER 16

DRUG

156

TABLE 16-5

TABLE 16-4 COMMON NONARRHYTHMIC TOXICITY OF MOST FREQUENTLY USED ANTIARRHYTHMIC AGENTS

PROARRHYTHMIC MANIFESTATIONS OF MOST FREQUENTLY USED ANTIARRHYTHMIC AGENTS

DRUG

COMMON NONARRHYTHMIC TOXICITY

DRUG

COMMON PROARRHYTHMIC TOXICITY

Amiodarone

Tremor, peripheral neuropathy, pulmonary inflammation, hypothyroidism and hyperthyroidism, photosensitivity Cough, flushing Anorexia, nausea, vomiting, visual changes Anticholinergic effects, decreased myocardial contractility Nausea Dizziness, nausea, headache, decreased myocardial contractility Nausea Dizziness, confusion, delirium, seizures, coma Ataxia, tremor, gait disturbances, rash, nausea Mood changes, tremor, loss of mental clarity, nausea, Lupus erythematosus–like syndrome (more common in slow acetylators), anorexia, nausea, neutropenia Taste disturbance, dyspepsia, nausea, vomiting Diarrhea, nausea, vomiting, cinchonism, thrombocytopenia Hypotension, bronchospasm

Amiodarone

Sinus bradycardia, AV block, increase in defibrillation threshold Rare: long QT and torsade de pointes, 1:1 ventricular conduction with atrial flutter All arrhythmias potentiated by profound pauses, atrial fibrillation High-grade AV block, fascicular tachycardia, accelerated junctional rhythm, atrial tachycardia Long QT and torsade de pointes, 1:1 ventricular response to atrial flutter; increased risk of some ventricular tachycardias in patients with structural heart disease Long QT and torsade de pointes 1:1 Ventricular response to atrial flutter; increased risk of some ventricular tachycardias in patients with structural heart disease; sinus bradycardia Long QT and torsade de pointes Long QT and torsade de pointes, 1:1 ventricular response to atrial flutter; increased risk of some ventricular tachycardias in patients with structural heart disease 1:1 Ventricular response to atrial flutter; increased risk of some ventricular tachycardias in patients with structural heart disease; sinus bradycardia Long QT and torsade de pointes, 1:1 ventricular response to atrial flutter; increased risk of some ventricular tachycardias in patients with structural heart disease Long QT and torsade de pointes, sinus bradycardia

Adenosine Digoxin Disopyramide Dofetilide Flecainide Ibutilide Lidocaine

SECTION III

Mexiletine Moricizine Procainamide

Heart Rhythm Disturbances

Propafenone Quinidine Sotalol

In patients with symptoms resulting from inadequate rate control with pharmacologic therapy or worsening LV function due to the persistent tachycardia, a His bundle/AV junction ablation can be performed. The ablation must be coupled with the implantation of an activity sensor pacemaker to maintain a physiologic range of heart rates. Recent evidence that RV pacing can occasionally modestly depress LV function should be taken into consideration in identifying which patients are appropriate candidates for the “ablate and pace” treatment strategy. Occasionally, biventricular pacing may be used to minimize the degree of dyssynchronization that can occur with RV apical pacing alone. Rate control treatment options must be coupled with chronic anticoagulation therapy in all cases. Trials evaluating the elimination of embolic risk by surgical elimination or isolation of the left atrial appendage or by endovascular insertion of a left atrial appendage– occluding device are ongoing and may provide other treatment options that can eliminate the need for chronic anticoagulation. CATHETER AND SURGICAL ABLATIVE THERAPY TO PREVENT RECURRENT AF Although

the optimum ablation strategy has not been defined,

Adenosine

Digoxin

Disopyramide

Dofetilide Flecainide

Ibutilide Procainamide

Propafenone

Quinidine

Sotalol

Note: AV, atrioventricular.

most ablation strategies incorporate techniques that isolate the atrial muscle sleeves entering the pulmonary veins; these muscle sleeves have been identified as the source of the majority of triggers responsible for the initiation of AF. Ablation therapy is currently considered an alternative to pharmacologic therapy in patients with recurrent symptomatic AF. Elimination of AF in 50–80% of patients with a catheter-based ablation procedure should be anticipated, depending on the chronicity of

VI

A

VI

particularly in patients with multiple risk factors for stroke, should be considered until guidelines are firmly established. If the left atrial appendage has been removed surgically, then the threshold for stopping anticoagulation should be lowered. Antiarrhythmic therapy typically can be discontinued after catheter or surgical ablation of AF. However, in selected patients, satisfactory AF control may require maintenance of previously ineffective drug therapy after the ablation intervention.

157

B

ATRIAL FLUTTER AND MACROREENTRANT ATRIAL TACHYCARDIAS VI

the AF, with additional patients becoming responsive to previously ineffective medications. Catheter ablative therapy also holds promise in patients with more persistent forms of AF and even those with severe atrial dilatation. If its efficacy is confirmed with additional study, it may also afford an important alternative to His bundle ablation and pacemaker insertion. Risks related to the left atrial ablation procedure, albeit low (overall 2–4%), include pulmonary vein stenosis, atrioesophageal fistula, systemic embolic events, and perforation/tamponade. Surgical ablation of AF is typically performed at the time of other cardiac valve or coronary artery surgery and, less commonly, as a stand-alone procedure. The Cox surgical Maze procedure is designed to interrupt all macroreentrant circuits that might potentially develop in the atria, thereby precluding the ability of the atria to fibrillate. In an attempt to simplify the operation, the multiple incisions of the traditional Cox-Maze procedure have been replaced with linear lines of ablation and pulmonary vein isolation using a variety of energy sources. Severity of AF symptoms and difficulties in rate and/or rhythm control with pharmacologic therapy will frequently dictate the optimum AF treatment strategy. Similar to the approach with pharmacologic rhythm control, a cautious approach to eliminating anticoagulant therapy is recommended after catheter or surgical ablation. Careful ECG monitoring for asymptomatic AF,

The Tachyarrhythmias

FIGURE 16-5 Atrial fibrillation (A) transitions to “slow” atrial flutter during antiarrhythmic drug therapy. (B) A rapid ventricular response with 1:1 atrioventricular conduction occurred with exercise, leading to (C) symptoms of dizziness.

CHAPTER 16

C

Macroreentrant arrhythmias involving the atrial myocardium are collectively referred to as AFL.The terms AFL and macroreentrant AT are frequently used interchangeably, with both denoting a nonfocal source of an atrial arrhythmia. The typical or most common AFL circuit rotates in a clockwise or counterclockwise direction in the right atrium around the tricuspid valve annulus.The posterior boundary of the right AFL circuit is defined by the crista terminalis, the Eustachian ridge, and the inferior and superior vena cava. Counterclockwise right AFL represents ∼80% of all AFL with superiorly directed activation of the interatrial septum, which produces the saw-toothed appearance of the P waves in ECG leads II, III, and aVF. Clockwise rotation of the same right atrial circuit produces predominantly positive P waves in leads II, III, and aVF (Fig. 16-4). Macroreentrant left AFL may also develop, albeit much less commonly. This type of arrhythmia may be the sequelae of surgical or catheterbased ablation procedures that create large anatomic barriers or promote slowing of conduction in the left atrium, especially around the mitral valve annulus. Atypical AFL or macroreentrant AT can also develop around incisions created during surgery for valvular or congenital heart disease or in and/or around large areas of atrial fibrosis. Classic or typical right AFL has an atrial rate of 260–300 beats/min with a ventricular response that tends to be 2:1, or typically 130–150 beats/min. In the setting of severe atrial conduction disease and or antiarrhythmic drug therapy, the atrial rate can slow to 5 cm left atrial diameter with a high risk of AF, and/or a history of coincident paroxysmal AF. Most focal ATs are readily amenable to catheter ablative therapy. In patients who fail to respond to medical therapy or who are reluctant to take chronic drug therapy, this option

160

II

II

II

II

VI

VI

VI

VI

Sinus node

* *

Atria

SECTION III

Slow pathway

AV node

Fast pathway

Ventricles

Heart Rhythm Disturbances

A

B

FIGURE 16-7 Pattern of atrial and ventricular activation and characteristic relationship of P wave and QRS complex as recorded in leads II and V1 during regular supraventricular tachycardias.

should be considered, with an anticipated 90% cure rate. A para-Hisian location for the AT and/or focus that is located in the left atrium may modestly increase the risk related to the procedure, and, for this reason, every effort should be made to determine the likely origin of the AT based on an analysis of the P wave morphology on 12-lead ECG prior to the procedure.

AV NODAL TACHYCARDIAS AV Nodal Reentrant Tachycardia AVNRT is the most common paroxysmal regular SVT. It is more commonly observed in women than men and is typically manifest in the second to fourth decades of life. In general, because AVNRT tends to occur in the absence of structural heart disease, it is usually well tolerated. In the presence of hypertension or other forms of structural heart disease that limit ventricular filing, hypotension or syncope may occur. AVNRT develops because of the presence of two electrophysiologically distinct pathways for conduction in the complex syncytium of muscle fibers that make up

C

D

A. Sinus tachycardia. B. Atrial tachycardia from top of the atria. C. Atrioventricular nodal reentry. D. Accessory pathway– mediated orthodromic supraventricular tachycardia.

the AV node. The fast pathway located in the more superior part of the node has a longer refractory period, while the pathway lower in the AV node region conducts more slowly but has a shorter refractory period. As a result of the inhomogeneities of conduction and refractoriness, a reentrant circuit can develop in response to premature stimulation. Although conduction occurs over both pathways during sinus rhythm, only the conduction over the fast pathway is manifest and, as a result, the PR interval is normal. APCs occurring at a critical coupling interval are blocked in the fast pathway because of the longer refractory period and are conducted slowly over the slow pathway. When sufficient conduction slowing occurs, the blocked fast pathway can recover excitability and atrial activation can occur over the fast pathway to complete the circuit. Repetitive activation down the slow and up the fast pathway results in typical AV nodal reentrant tachycardia (Fig. 16-7). ECG Findings in AVNRT

The APC initiating AVNRT is characteristically followed by a long PR interval consistent with conduction via the slow pathway. AVNRT is manifest typically as a narrow QRS complex tachycardia at rates that range

from 120–250 beats/min.The QRS-P wave pattern associated with typical AVNRT is quite characteristic, with simultaneous activation of the atria and ventricles from the reentrant AV nodal circuit.The P wave will frequently be buried inside the QRS complex and either not be visible or will distort the initial or terminal portion of the QRS complex (Fig. 16-7). Because, atrial activation originates in the region of the AV node, a negative deflection will be generated by retrograde atrial depolarization. Occasionally, AVNRT occurs with activation in the reverse direction, conducting down the fast pathway and returning up the slow pathway. This form of AVNRT occurs much less commonly and produces a prolonged RP interval during the tachycardia with a negative P wave in leads 2, 3, and aVF.This atypical form of AVNRT is more easily precipitated by ventricular stimulation.

PREVENTION Prevention may be achieved with drugs that slow conduction in the antegrade slow pathway, such as digitalis, beta blockers, or calcium channel blockers. In patients who have a history of exerciseprecipitated AVNRT, the use of beta blockers frequently eliminates symptoms. In patients who do not respond to drug therapy directed at the antegrade slow pathway, treatment with class IA or IC agents directed at altering conduction of the fast pathway may be considered. Catheter ablation, directed at elimination or modification of slow pathway conduction, is very effective in permanently eliminating AVNRT. Patients with recurrent AVNRT that produces significant symptoms or heart rates >200 beats/min and patients reluctant to take chronic drug therapy should be considered for ablative therapy. Catheter ablation can cure AV nodal reentry in >95% of patients. The risk of AV block requiring a permanent pacemaker is ∼1% with the ablation procedure. This risk may be further minimized with the use of cryoablation techniques when the slow pathway is in close proximity to the compact AV node.

Treatment: ATRIOVENTRICULAR JUNCTIONAL TACHYCARDIAS

Treatment of automatic/triggered junctional tachycardias is directed at decreasing adrenergic stimulation and reversing digoxin toxicity, if present. Digoxin therapy can be withheld if toxicity is suspected, and the administration of digoxin-specific antibody fragments can rapidly reverse digoxin toxicity if the tachycardia is producing significant symptoms and rapid termination is indicated. Junctional tachycardia due to abnormal automaticity can be treated pharmacologically with beta blockers. A trial of class IA or IC drugs may also be attempted. For incessant automatic junctional tachycardia, focal catheter ablation can be performed but is associated with an increased risk of AV block.

TACHYCARDIAS ASSOCIATED WITH ACCESSORY AV PATHWAYS Tachycardias that involve accessory pathways (APs) between atria and ventricles commonly manifest a normal QRS complex with a short or long RP interval. They must be considered in the differential diagnosis of other narrow-complex tachycardias. Importantly, most tachycardias associated with APs involve a large macroreentrant

The Tachyarrhythmias

Treatment is directed at altering conduction within the AV node. Vagal stimulation, such as occurs with the Valsalva maneuver or carotid sinus massage, can slow conduction in the AV node sufficiently to terminate AVNRT. In patients in whom physical maneuvers do not terminate the tachyarrhythmia, the administration of adenosine, 6–12 mg IV, frequently does so. Intravenous beta blockade or calcium channel therapy should be considered second-line agents. If hemodynamic compromise is present, R wave synchronous DC cardioversion using 100–200 J can terminate the tachyarrhythmia.

ACUTE TREATMENT

These can also occur in the setting of enhanced normal automaticity, abnormal automaticity, or triggered activity. These tachycardias may or may not be associated with retrograde conduction to the atria, and the P waves may appear dissociated or produce intermittent conduction and early activation of the junction. These arrhythmias may occur as a manifestation of increased adrenergic tone or drug effect in patients with sinus node dysfunction or following surgical or catheter ablation. The arrhythmia may also be a manifestation of digoxin toxicity. The most common manifestation of digoxin intoxication is the sudden regularization of the response to AF. A junctional tachycardia due to digoxin toxicity typically does not manifest retrograde conduction. Sinus activity may appear dissociated or result in intermittent capture beats with a long PR interval. If the rate is >50 beats/min and 200 beats/min with SVT should be given strong consideration for undergoing catheter ablation. Patients who have demonstrated rapid antegrade conduction over their AP or the potential for rapid conduction should also be considered for catheter ablation. Catheter ablation therapy has been demonstrated to be successful in >95% of patients with documented WPW syndrome and appears effective regardless of age. The risk of catheter ablative therapy is low and is dictated primarily by the location of the AP. Ablation of para-Hisian APs is associated with a risk of heart block, and ablation in the left atrium is associated with a small but definite risk of thromboembolic phenomenon.These risks must be weighed against the potential serious complications associated with hemodynamic compromise, the risk of VF, and the severity of the patient’s symptoms with AP-mediated tachycardias. Patients who demonstrate evidence of ventricular preexcitation in the absence of any prior arrhythmia history deserve special consideration. The first arrhythmia manifestation can be a rapid SVT or, albeit of low risk (140 ms in duration. VPCs are common and increase with age and the presence of structural heart disease.VPCs can occur with a certain degree of periodicity that has become incorporated into the lexicon of electrocardiography. VPCs may occur in patterns of bigeminy, in which every sinus beat is followed by a VPC, or trigeminy, in which two sinus beats are followed by a VPC. VPCs may have different morphologies and are thus referred to as multiformed. Two successive VPCs are termed pairs or couplets.Three or more consecutive VPCs are termed VT when the rate is >100 beats/min. If the repetitive VPCs terminate spontaneously and are more than three beats in duration, the arrhythmia is referred to as nonsustained VT. APCs with aberrant ventricular conduction may also create a wide and early QRS complex. The premature P wave can occasionally be difficult to discern when it falls on the preceding T wave, and other clues must be used to make the diagnosis.The QRS pattern for a VPC does not appear to follow a typical right or left bundle branch block pattern as the QRS morphology is associated with aberrant atrial conduction and can be quite bizarre. On occasion,VPCs can arise from the Purkinje network of the ventricles, in which case the QRS pattern mimics aberration. The 12-lead ECG recording of the VPC may be required to identify subtle morphologic clues regarding the QRS complex to confirm its ventricular origin. Most commonly,VPCs are associated with a “fully compensatory pause”; i.e., the duration between the last QRS before the PVC and the next QRS complex is equal to twice the sinus rate (Fig. 16-3). The VPC typically does not conduct to the atrium. If the VPC does conduct to the atrium, it may not be sufficiently early to reset the sinus node. As a result, sinus activity will occur and the antegrade wavefront from the sinus node may encounter some delay in the AV node or His-Purkinje system from the blocked VPC wavefront, or it may collide with the retrograde atrial wavefront. Sinus activity will continue undisturbed, resulting in a delay to the next QRS complex (Fig. 16-3). Occasionally the VPC can occur early enough and conduct retrograde to the atrium to reset the sinus node; the pause that results will be less than compensatory. VPCs that fail to influence the oncoming sinus impulse are termed interpolated VPCs. A ventricular focus that fires repetitively at a fixed interval may produce variably coupled VPCs, depending on the sinus rate.This type of focus is referred to as a parasystolic focus because its firing

does not appear to be modulated by sinus activity and the conducted QRS complex. The ventricular ectopy will occur at a characteristic fixed integer or multiple of these intervals.The variability in coupling relative to the underlying QRS complex and a fixed interval between complexes of ventricular origin provide the diagnostic information necessary to identify a parasystolic focus.

Treatment: VENTRICULAR PREMATURE COMPLEXES

The threshold for treatment of VPCs is high, and the treatment is primarily directed at eliminating severe symptoms associated with palpitations. VPCs of sufficient frequency can cause a reversible cardiomyopathy. Depressed LV function in the setting of ventricular bigeminy and/or frequent nonsustained VT should raise the possibility of a cardiomyopathy that is reversible with control of the ventricular arrhythmia. In the absence of structural heart disease, VPCs do not appear to have prognostic significance. In patients with structural heart disease, frequent VPCs and runs of nonsustained VT have prognostic significance and may portend an increased risk of SCD. However, no study has documented that elimination of VPCs with antiarrhythmic drug therapy reduces the risk of arrhythmic death in patients with severe structural heart disease. Drug therapies that slow myocardial conduction and/or enhance dispersion of refractoriness can actually increase the risk of life-threatening arrhythmias (drug-induced QT prolongation and TdP) despite being effective at eliminating VPCs.

ACCELERATED IDIOVENTRICULAR RHYTHM (AIVR) AIVR refers to a ventricular rhythm that is characterized by three or more complexes at a rate >40 beats/min and 100 beats/min; most have rates >120 beats/min. Sustained VT at rates 140 ms in the absence of drug therapy, (2) a superior and rightward QRS frontal plane axis, (3) a bizarre QRS complex that does not mimic the characteristic QRS pattern associated with left or right bundle branch block, and (4) slurring of the initial portion of the QRS (Fig. 16-10). Table 16-6 provides a useful summary of ECG criteria that have evolved based on the described characteristics of VT.

Treatment: VENTRICULAR TACHYCARDIA/ FIBRILLATION

Sustained polymorphic VT, ventricular flutter, and VF all lead to immediate hemodynamic collapse. Emergency asynchronous defibrillation is therefore required, with at least 200-J monophasic or 100-J biphasic shock. The shock should be delivered asynchronously to avoid delays related to sensing of the QRS complex. If the arrhythmia persists, repeated shocks with the maximum energy output of the defibrillator are essential to optimize the chance of successful resuscitation. Intravenous lidocaine and/or amiodarone should be administered but should not delay repeated attempts at defibrillation. For any monomorphic wide complex rhythm that results in hemodynamic compromise, a prompt R wave synchronous shock is required. Conscious sedation should be provided if the hemodynamic status permits. For patients with a well-tolerated wide complex tachycardia, the appropriate diagnosis should be established based on strict ECG criteria (Table 16-6). Pharmacologic treatment to terminate monomorphic VT is not typically successful (200 ms, superior frontal plane axis, slurring of the initial portion of the QRS, and

large S wave in V6—all clues to the diagnosis of ventricular tachycardia.

TABLE 16-6 ECG CLUES SUPPORTING THE DIAGNOSIS OF VENTRICULAR TACHYCARDIA

Note: AV, atrioventricular; RBBB/LBBB, right/left bundle branch block.

Chart speed 25.0 mm/sec

Atria

Ventricle AF

VT

Pacing

FIGURE 16-11 Ventricular tachycardia (VT) (*) during atrial fibrillation stopped by pacing (#) from an implantable cardioverter defibrillator (ICD) from recording stored by ICD. The atrial electrogram shows characteristic fibrillatory waves through the tracing. The ventricular electrogram shows an irregularly irregular response consistent with atrial fibrillation at the

AF

beginning of the tracing. The ventricular electrogram suddenly changes in morphology (*) and becomes regular, consistent with the diagnosis of VT. Pacing transiently accelerates the rate and interrupts the rapid VT. The patient was unaware of the life-threatening event.

The Tachyarrhythmias

synchronous R wave cardioversion after the administration of conscious sedation is appropriate. Selected patients with focal outflow tract tachycardias (p. 169) who demonstrate triggered or automatic VT may respond to IV beta blocker administration. Idiopathic LV septal VT (see p. 169) appears to respond uniquely to IV verapamil administration. VT in patients with structural heart disease is now almost always treated with the implantation of an ICD to manage anticipated VT recurrence. The ICD can

167

CHAPTER 16

AV dissociation (atrial capture, fusion beats) QRS duration >140 ms for RBBB type V1 morphology; V1 >160 ms for LBBB type V1 morphology Frontal plane axis –90° to 180° Delayed activation during initial phase of the QRS complex LBBB pattern—R wave in V1, V2 >40 ms RBBB pattern—onset of R wave to nadir of S >100 ms Bizarre QRS pattern that does not mimic typical RBBB or LBBB QRS complex Concordance of QRS complex in all precordial leads RS or dominant S in V6 for RBBB VT Q wave in V6 with LBBB QRS pattern Monophasic R or biphasic qR or R/S in V1 with RBBB pattern

provide rapid pacing and shock therapy to treat most VTs effectively (Fig. 16-11). Prevention of VT remains important, and >50% of patients with a history of VT and an ICD may need to be treated with adjunctive antiarrhythmic drug therapy to prevent VT recurrences or to manage atrial arrhythmias. Because of the presence of an ICD, there is more flexibility with respect to antiarrhythmic drug therapy selection. The use of sotalol or amiodarone represents first-line therapy for patients with a history of structural heart disease and life-threatening monomorphic or polymorphic VT not due to long QT syndrome. Importantly, sotalol has been associated with a decrease in the defibrillation threshold, which reflects the amount of energy necessary to terminate VF. Amiodarone may be better tolerated in patients with a more marginal hemodynamic status and systolic blood pressure. The risk of end organ toxicity from amiodarone must be weighed against the ease of use and general efficacy. Antiarrhythmic drug therapy with agents such as quinidine, procainamide, or propafenone, which might not normally be used in patients with structural heart disease because of the risk of proarrhythmia, may be considered in patients with an ICD and recurrent VT. Catheter ablative therapy for VT in patients without structural heart disease results in cure rates >90%. In patients with structural heart disease, catheter ablation that includes a strategy for eliminating unmappable/rapid VT and one that incorporates endocardial as well as epicardial mapping and ablation should be employed. In most patients, catheter ablation can reduce or eliminate

168

the requirement for toxic drug therapy and should be considered in any patient with recurrent VT. The utilization of ablative therapy to reduce the incidence of ICD shocks for VT in patients who receive the ICD as part of primary prevention for VT is being actively investigated. Repeated VT episodes requiring external cardioversion/defibrillation or repeated appropriate ICD shock therapy is referred to as VT storm.While a definition of more than two episodes in 24 h is used, most patients with VT storm will experience many more episodes. In the extreme form of VT storm, the tachycardia becomes incessant and the baseline rhythm is unable to be restored for any extended period. In patients with recurrent polymorphic VT in the absence of the long QT interval, one should have a high suspicion of active ischemic disease or fulminant myocarditis. Intravenous lidocaine or amiodarone administration should be coupled with prompt assessment of the status of the coronary anatomy. Endomyocardial biopsy, if indicated by clinical circumstance, may be used to confirm the diagnosis of myocarditis, although the diagnostic yield is low. In patients who demonstrate QT prolongation and recurrent pausedependent polymorphic VT (TdP), removal of an offending QT-prolonging drug, correction of potassium or magnesium deficiencies, and emergency pacing to prevent pauses should be considered. Intravenous beta blockade therapy should be considered for polymorphic VT storm. A targeted treatment strategy should be employed if the diagnosis of the polymorphic VT syndrome can be established. For example, quinidine or isoproterenol can be used in the treatment of Brugada’s syndrome (p. 174). Intra-aortic balloon counterpulsation or acute coronary angioplasty may be needed to stop recurrent polymorphic VT precipitated by acute ischemia. In selected patients with a repeating VPC trigger for their polymorphic VT, the VPC can be targeted for ablation to prevent recurrent VT. In patients with recurrent monomorphic VT, acute IV administration of lidocaine, procainamide, or amiodarone can prevent recurrences. The use of such therapy is empirical, and a clinical response is not certain. Procainamide and amiodarone are more likely to slow the tachycardia and make it hemodynamically tolerated. Unfortunately, antiarrhythmic drugs, especially those that slow conduction (e.g., amiodarone, procainamide), can also facilitate recurrent VT or even result in incessant VT. VT catheter ablation can eliminate frequent recurrent or incessant VT and frequent ICD shocks. Such therapy should be deployed earlier in the course of arrhythmia events to prevent adverse consequences of recurrent VT episodes and adverse effects from antiarrhythmic drugs.

MANAGEMENT OF VT STORM

UNIQUE VT SYNDROMES Although most ventricular arrhythmias occur in the setting of coronary artery disease with prior myocardial infarction, a significant number of patients develop VT in other settings. A brief discussion of each unique VT syndrome is warranted. Information that illustrates a unique pathogenesis and enhances the ability to make the correct diagnosis and institute appropriate therapy will be highlighted. Idiopathic Outflow Tract VT

SECTION III Heart Rhythm Disturbances

VT in the absence of structural heart disease is referred to as idiopathic VT.There are two major varieties of these VTs. Outflow tachycardias originate in the RV and LV outflow tract regions. Approximately 80% of outflow tract VTs originate in the RV and ∼20% in the LV outflow tract regions. Outflow tract VTs appear to originate from anatomic sites that form an arc beginning just above the tricuspid valve and extending along the roof of the outflow tract region to include the free wall and septal aspect of the right ventricle just beneath the pulmonic valve, the aortic valve region, and then the anterior/superior margin of the mitral valve annulus. These arrhythmias appear more commonly in women. Importantly, these ventricular arrhythmias are not associated with SCD. Patients manifest symptoms of palpitations with exercise, stress, and caffeine ingestion. In women, the arrhythmia is more commonly associated with hormonal triggers and can frequently be timed to the premenstrual period, gestation, and menopause. Uncommonly, the VPCs and VTs can be of sufficient frequency and duration to cause a tachycardia-induced cardiomyopathy. The pathogenesis of outflow tract VT remains unknown, and there is no definite anatomic abnormality identified with these VTs. Vagal maneuvers, adenosine, and beta blockers tend to terminate the VTs, whereas catecholamine infusion, exercise, and stress tend to potentiate the outflow tract VTs. Based on these observations, the mechanism of the arrhythmia is most likely calcium-dependent triggered activity. Preliminary data suggest that at least in some patients, a somatic mutation of the inhibitory G protein (Gα I2) may serve as the genetic basis for the VT. In contrast to VT in patients with coronary artery disease, outflow tract VTs are uncommonly initiated with programmed stimulation but are able to be initiated by rapid-burst atrial or ventricular pacing, particularly when coupled with the infusion of isoproterenol. Outflow tract VT typically produces large monophasic R waves in the inferior frontal plane leads II, III, and aVF, and typically occurs as nonsustained bursts of VT and/or frequent premature beats. Cycle length oscillations

during the tachycardia are common. Since most VT originates in the RV outflow tract, the VT typically has a left bundle branch block pattern in lead V1 (negative QRS vector) (Fig. 16-12). Outflow tract VT, originating in the left ventricle, particularly those associated with an origin from the mitral valve annulus, have a right bundle branch block pattern in lead V1 (positive QRS vector).

Idiopathic IV Septal VT

RVOT-VT

I

Idiopathic LV Septal/Fascicular VT

II

VI

II

The second most common idiopathic VT is linked anatomically to the Purkinje system in the left ventricle. The arrhythmia mechanism appears to be macroreentry involving calcium-dependent slow response fibers that are part of the Purkinje network, although automatic tachycardias have also been observed. A 12-lead ECG morphology of the VT shows a narrow right bundle branch block pattern and a superior leftward axis or an inferior rightward axis, depending upon whether the VT originates from the posterior or anterior fascicles (Fig. 16-12). Idiopathic LV septal VT is unique in its suppression with verapamil. Beta blockers have also been used with some success as primary or effective adjunctive therapy. Catheter ablation is very effective therapy for VT resistant to drug therapy or in patients reluctant to take daily therapy, with anticipated successful elimination of VT in >90% of patients.

VI

VT Associated with LV Dilated Cardiomyopathy FIGURE 16-12 Common idiopathic ventricular tachycardia (VT) ECG patterns. Right ventricular outflow tract (RVOT) VT with typical left bundle QRS pattern in V1 and inferiorly directed frontal plane axis, and left ventricular septal VT from the inferior septum with a narrow QRS right bundle branch block pattern in V1 and superior and leftward front plane QRS axis.

Monomorphic and polymorphic VTs may occur in patients with nonischemic dilated cardiomyopathy (Chap. 21). Although the myopathic process may be diffuse, there appears to be a predilection for the development of fibrosis around the mitral and aortic valvular regions. Most uniform sustained VT can be mapped to these regions of fibrosis. Drug therapy is usually

The Tachyarrhythmias

Acute medical therapy for idiopathic outflow tract VT is rarely required because the VT is hemodynamically tolerated and is typically nonsustained. Intravenous beta blockers frequently terminate the tachycardia. Chronic therapy with beta or calcium channel blockers frequently prevents recurrent episodes of the tachycardia. The arrhythmia also appears to respond to treatment with class IA or IC agents or with sotalol. In patients who are reluctant to take long-term drug therapy or who have persistent symptoms despite drug therapy, catheter ablative therapy has been utilized successfully to eliminate the tachycardia with success rates >90%. Because of the absence of structural heart disease and the focal nature of these arrhythmias, the 12-lead ECG pattern during VT can help localize the site of origin of the arrhythmia and help facilitate catheter ablation. Efficacy of therapy is assessed with treadmill testing and/or ECG monitoring, and electrophysiologic study is performed only when the diagnosis is in question or to perform catheter ablation.

169

CHAPTER 16

I

Treatment: IDIOPATHIC OUTFLOW TRACT VENTRICULAR TACHYCARDIA

170 ineffective in preventing VT, and empirical trials of sotalol or amiodarone are usually initiated only for recurrent VT episodes after ICD implantation. VT associated with nonischemic dilated cardiomyopathy appears to be less amenable to catheter ablative therapy from the endocardium; frequently, the VT originates from epicardial areas of fibrosis and catheter access to the epicardium can be gained via a percutaneous pericardial puncture to improve the outcome of ablation techniques. In patients with a history of depressed myocardial dysfunction due to a nonischemic cardiomyopathy with an LV ejection fraction 30 mm, or nonsustained spontaneous VT, the risk of SCD is high and ICD implantation is usually indicated. Amiodarone, sotalol, and beta blockers have been used to control recurrent VT. Experience with ablative therapy is limited because of the infrequency with which the VT is tolerated hemodynamically. Ablation procedures that target the substrate for VT/VF and ablate areas of low voltage consistent with fibrosis appear to have promise in this setting. The WPW syndrome has been observed in patients with hypertrophic cardiomyopathy associated with PRKAG2 mutations. VT Associated with Other Infiltrative Cardiomyopathies and Neuromuscular Disorders An increased arrhythmia risk has been identified when cardiac involvement occurs in a variety of infiltrative diseases and neuromuscular disorders (Table 16-7). Many patients manifest AV conduction disturbances and may require permanent pacemaker insertion.The decision to implant an ICD device should follow current established guidelines for patients with nonischemic cardiomyopathy, which include a history of syncope with depressed LV function, a history of severely depressed LV function,

TABLE 16-7 INFILTRATIVE/INFLAMMATORY AND NEUROMUSCULAR DISORDERS ASSOCIATED WITH AN INCREASED VENTRICULAR ARRHYTHMIA RISK Sarcoidosisa Chagas diseasea Amyloidosisa Fabry disease Hemochromatosis Myotonic muscular dystrophya

Emery-Dreyfuss muscular dystrophya Limb-girdle muscular dystrophya Duchenne’s muscular dystrophy Becker’s muscular dystrophy Kearn-Sayre syndromea Friedreich’s ataxia

a

High frequency of ventricular arrhythmias noted.

(See also Chap. 21) ARVCM/D, due to a genetically determined dysplastic process or after a suspected viral myocarditis, is also associated with VT/VF. The sporadic

V1

V1

The Tachyarrhythmias

Arrhythmogenic RV Cardiomyopathy/ Dysplasia (ARVCM/D)

CHAPTER 16

and LV ejection fraction 500 ms is clearly associated with a greater arrhythmia risk in patients with the LQTS. Many affected individuals may have QT intervals that intermittently measure within a normal range or that fail to shorten appropriately with exercise. Some individuals will only manifest the syndrome when exposed to a drug, such as sotalol, that alters channel function. The genotype associated with the LQTS appears to influence prognosis, and identification of the genotype appears to help to optimize clinical management. The first three genotypic designations of the mutations identified, LQT1, LQT2, and LQT3, appear to account for >99% of patients with clinically relevant LQTSs. Surface ECG characteristics may be helpful in distinguishing the three most common genotypes, with genetic testing being definitive. LQT1 represents the most common genotypic abnormality. Patients with LQT1 fail to shorten or actually prolong their QT interval with exercise. The T wave in patients with LQT1 tends to be broad and comprises the majority of the prolonged QT interval. The most common triggers for potentiating cardiac arrhythmias in patients with LQT1 are exercise followed by emotional stress. More than 80% of male patients have their first cardiac event by 20 years, so competitive exercise should be restricted and swimming avoided for these patients. Patients tend to respond to beta blocker therapy. Patients with two LQT1 alleles have the Jervell and Lange-Neilsen

TABLE 16-8 INHERITED ARRHYTHMIA DISORDERS—“CHANNELOPATHIES” WITH HIGH RISK OF VENTRICULAR ARRHYTHMIAS DISORDER

GENE

PROTEIN/CHANNEL AFFECTED

LQT1 LQT2 LQT3 LQT4 LQT5 LQT6 LQT7 LQT8 Jervell LN1 Jervell LN2 Brugada syndrome Catecholaminergic VT

KCNQ1 KCNH2 (HERG) SCN5A ANK2 KCNE1 KCNE2 KCNJ2 CACNA1C KCNQ1 KCNE1 SCN5A Ry R2

SQTS1 SQTS2 SQTS3

KCNH2 (HERG) KCNQ1 (KvLQT1) KCNJ2

IKs channel α subunit IKr channel α subunit INa channel α subunit Ankyrin-B IKs channel β subunit IKr channel β subunit IK1 channel α subunit ICa channel α subunit IKs channel β subunit IKr channel β subunit INa channel Ryanodine receptor, calsequestron receptor IKr channel α subunit IKs channel α subunit IK1 channel

Note: LQT, long QT (interval); SQT, short QT (interval).

174 syndrome, with more dramatic QT prolongation and

SECTION III

deafness and a worse arrhythmia prognosis. LQT2 is the second most common genotypic abnormality. The T wave tends to be notched and bifid. In LQT2 patients, the most frequent precipitant is emotional stress, followed by sleep or auditory stimulation. Despite the occurrence during sleep, patients typically respond to beta blocker therapy. LQT3 is due to a mutation in the gene that encodes the cardiac sodium channel located on chromosome 3. Prolongation of the action potential duration occurs because of failure to inactivate this channel. LQT3 patients either have late-onset peaked biphasic T waves or asymmetric peaked T waves.The arrhythmia events tend to be more life-threatening, and thus the prognosis for LQT3 is the poorest of all the LQTs. Male patients appear to have the worst prognosis in patients with LQT3. Most events in LQT3 patients occur during sleep, suggesting that they are at higher risk during slow heart rates. Beta blockers are not recommended, and exercise is not restricted in LQT3.

and/or alterations in elimination kinetics because of hepatic or renal dysfunction frequently contribute to the arrhythmias.

Treatment: ACQUIRED LONG QT SYNDROME

Acute therapy for acquired LQTS is directed at eliminating the offending drug therapy, reversing metabolic abnormalities by the infusion of magnesium and/or potassium, and preventing pause-dependent arrhythmias by temporary pacing or the cautious infusion of isoproterenol. Class IB antiarrhythmic agents (e.g., lidocaine), which do not cause QT prolongation, may also be used, though they are frequently ineffective. Supportive therapy to allay anxiety and prevent pain with required DC shock therapy for sustained arrhythmias as well as efforts to facilitate drug elimination are important.

Short QT Syndrome

Heart Rhythm Disturbances

Treatment: LONG QT SYNDROME

The institution of ICD therapy should be strongly considered in any patient with LQTS who has demonstrated any life-threatening arrhythmia. Patients with syncope with a confirmed diagnosis based on unequivocal ECG criteria or positive genetic testing should also be given the same strong consideration. Primary prevention with prophylactic ICD implantation should be considered in male patients with LQT3 and in all patients with marked QT prolongation (>500 ms), particularly when coupled with an immediate family history of SCD. Future epidemiologic investigation may provide firmer guidelines to sort patients further based on risks such as age, gender, arrhythmia history, and genetic characteristics. In all patients with documented or suspected LQTS, drugs that prolong the QT interval must be avoided. For an updated list of drugs, go to www.qtdrugs.org.

Acquired LQTS Patients with a genetic predisposition related to what appear to be sporadic mutations and/or single nucleotide polymorphisms can develop marked QT prolongation in response to drugs that alter repolarization currents. The QT prolongation and associated polymorphic ventricular tachycardia (TdP) are more frequently seen in women and may be a manifestation of subclinical LQTS. Druginduced long QT and TdP are frequently potentiated by the development of hypokalemia and bradycardia. The offending drugs typically block the potassium IKr channel (Table 16-5). Since most drug effects are dose-dependent, important drug-drug interactions that alter metabolism

A gain in function of repolarization currents can result in a shortening of atrial and ventricular refractoriness and marked QT shortening on the surface ECG (Table 16-8). The T wave tends to be tall and peaked. A QT interval 90 g/d) of alcohol over many years may develop a clinical picture resembling idiopathic or familial DCM.The risk of developing cardiomyopathy is partially determined genetically. A polymorphism of the gene encoding the alcohol metabolizing enzyme, alcohol dehydrogenase (ALDH2∗2), as well as the DD form of the angiotensin-converting enzyme (ACE) gene increase the predilection for the development of alcoholic cardiomyopathy. Patients with advanced alcoholic cardiomyopathy and severe CHF have

NEUROMUSCULAR DISEASE Cardiac involvement is common in many of the muscular dystrophies. In Duchenne’s progressive muscular dystrophy, mutations in a gene that encodes a cardiac structural protein (dystrophin) lead to myocyte death. Myocardial involvement is most frequently indicated by a distinctive and unique ECG pattern consisting of tall R waves in the right precordial leads with an R/S ratio >1.0, often associated with deep Q waves in the limb and lateral precordial leads. A variety of supraventricular and

ventricular arrhythmias is frequently found. Rapidly progressive HF may develop despite extended periods of apparent circulatory stability. Myotonic dystrophy is characterized by a variety of ECG abnormalities, especially disorders of impulse formation and AV conduction, but other overt clinical evidence of heart disease is uncommon. Because of these abnormalities, syncope and sudden death are major hazards. In appropriate patients, insertion of an ICD and/or permanent pacemaker may be effective.

DRUGS

ARRHYTHMOGENIC RIGHT VENTRICULAR CARDIOMYOPATHY/DYSPLASIA (ARVCM/D)

TAKO-TSUBO (STRESS) CARDIOMYOPATHY Also known as apical ballooning syndrome, this uncommon cardiac syndrome is characterized by the abrupt onset of severe chest discomfort preceded by a very stressful

Cardiomyopathy and Myocarditis

ARVCM/D is a familial cardiomyopathy characterized by progressive fibrofatty replacement of the right ventricle and, to a much lesser degree, of the LV myocardium. It is most commonly inherited in an autosomal dominant manner and is caused by multiple mutations of several genes encoding proteins that constitute desmosomes, structures that maintain normal contacts between cells. It has been suggested that abnormalities in the desmosomes cause detachment of myocytes with consequent myocyte apoptosis and fibrofatty replacement. Among the desmosomal protein genes, the most common gene mutation occurs in plakophilin-2 (PKP-2). Mutations in the cardiac ryanodine receptor gene (RyR2) and other genes have also been described. On clinical examination, patients may manifest RV failure with jugular venous distention, hepatomegaly, and edema. Clinical manifestations usually develop during the second decade and include ventricular tachyarrhythmias as well as varying degrees of RV failure; both of these complications may be fatal. The ECG typically shows QRS prolongation localized to the right precordial leads and left bundle branch block–type ventricular tachycardia. CTI and CMRI typically show RV dilatation, RV aneurysm, and fatty replacement (Fig. 21-2). Restriction from competitive sports and antiarrhythmic therapy with beta blockers or amiodarone may be useful. Implantation of an ICD may be required (Chap. 16). If RV failure becomes intractable, cardiac transplantation (Chap. 18) may be necessary.

CHAPTER 21

A variety of pharmacologic agents may damage the myocardium acutely, producing a pattern of inflammation (myocarditis, see later), or they may lead to chronic damage of the type seen with DCM. Certain drugs produce only ECG abnormalities, while others may precipitate fulminant CHF and death. The anthracycline derivatives, particularly doxorubicin (Adriamycin), are powerful antineoplastic agents. Systolic dysfunction and ventricular arrhythmias occur in a dose-dependent manner with a dose >450 mg/m2 and are frequent with doses >550 mg/m2. The development of these complications appears to be related to damage to the inner mitochondrial membrane and interference with the synthesis of adenosine triphosphate. This development is related not only to the dose of the drug but also to the presence or absence of several risk factors, which include cardiac irradiation, underlying heart disease, hypertension, and concurrent treatment with cyclophosphamide. At any dose of doxorubicin, patients with these risk factors have a greater frequency of developing HF than do patients lacking them. Doxorubicin cardiotoxicity may occur acutely but more commonly develops a median of 3 months after the last dose. In others, late contractile dysfunction may develop years after doxorubicin administration. By measuring cardiac-specific troponin and monitoring LV function with radionuclide ventriculography or echocardiography, usually combined with exercise stress, it is possible to document preclinical deterioration of LV function and allow appropriate dose adjustments. Also, monitoring may make it possible to continue doxorubicin even in patients at high risk for developing HF. Efforts to modify the dose schedule by giving the drug more slowly, along with the selective use of potentially cardioprotective agents such as the iron-chelator dexrazoxone, have reduced the risk of cardiotoxicity. Some patients have demonstrated recovery of cardiac function with aggressive management using ACE inhibitors. Trastuzumab (Herceptin), used in the treatment of breast cancer, causes cardiomyopathy in 7% of patients when used as monotherapy and four times as frequently when combined with doxorubicin. High-dose cyclophosphamide may produce CHF acutely or within 2 weeks of

administration; a characteristic histopathologic feature is 245 myocardial edema and hemorrhagic necrosis. LV dysfunction has also been reported with the administration of the nonreceptor tyrosine kinase inhibitor imatinib mesylate (Gleevec), used in the treatment of chronic myeloid leukemia. ECG changes and arrhythmias may result from treatment with tricyclic antidepressants, the phenothiazines, emetine, lithium, and various aerosol propellants. Cocaine abuse is associated with a variety of life-threatening cardiac complications, including SCD, myocarditis, DCM, and acute myocardial infarction (resulting from coronary spasm and/or thrombosis with or without underlying coronary artery disease). Nitrates, calcium channel blockers, antiplatelet agents, and benzodiazepines have been used to treat cocaine-induced cardiotoxicities.

arrest of normal embryogenesis, with the persistence of the deep recesses and sinusoids in the myocardium that characterize the embryonic heart. These sinusoids and associated spongy network of myocardial fibers ordinarily undergo organization and “compaction” early in embryonic life; when this fails to occur, LVNC results. This condition is diagnosed on echocardiography by the demonstration of multiple deep trabeculations into the myocardium, all of which communicate with the ventricular cavity, associated with LV contractile dysfunction. Standard therapy for CHF is routinely employed, typically along with chronic anticoagulation.

246

HYPERTROPHIC CARDIOMYOPATHY

SECTION IV

FIGURE 21-2 Cardiac MRI showing right ventricular (RV) enlargement (left) and fatty replacement of the RV myocardium (black arrows) of a patient with arrhythmogenic RV dysplasia. (From S Sen-Chowdhry et al: Am J Med 117:685, 2004; with permission.)

Disorders of the Heart

emotional or physical event. It occurs most commonly in women >50 years and is accompanied by ST-segment elevations and/or deep T-wave inversions in the precordial leads. No obstruction in the epicardial coronary arteries is noted on angiography.There is severe akinesia of the distal portion of the left ventricle with reduction of the EF. Troponins are usually mildly elevated. Cardiac imaging typically shows “ballooning” of the left ventricle in end-systole, especially of the LV apex. All of these changes, which are often quite dramatic, are reversible within 3–7 days and do not cause long-term cardiac dysfunction or disability. The mechanism responsible for Tako-tsubo cardiomyopathy is not clear, although it is likely that an adrenergic surge that includes circulating catecholamines, acting on the epicardial coronary vessels and/or coronary microcirculation, is involved. Although beta blockers are used in therapy, there is no definitive evidence that they are beneficial.

LEFT VENTRICULAR NONCOMPACTION Left ventricular noncompaction (LVNC) is a recently characterized uncommon congenital cardiomyopathy that may present at any age with symptoms of CHF, thromboembolism, or ventricular arrhythmias. It results from the

Hypertrophic cardiomyopathy (HCM) is characterized by LV hypertrophy, typically of a nondilated chamber, without obvious cause, such as hypertension or aortic stenosis. It is found in about 1 in 500 of the general population. Two features of HCM have attracted the greatest attention: (1) asymmetric LV hypertrophy, often with preferential hypertrophy of the interventricular septum; and (2) a dynamic LV outflow tract pressure gradient, related to narrowing of the subaortic area. About one-third of patients with HCM demonstrate an outflow tract pressure gradient at rest and a similar fraction develop one with provocation. The ubiquitous pathophysiologic abnormality is diastolic dysfunction, which can be detected by Doppler tissue imaging and results in elevated LV enddiastolic pressures; the latter may be present despite a hyperdynamic, nondilated LV. The pattern of hypertrophy is distinctive in HCM and usually differs from that seen in secondary hypertrophy (as in hypertension or aortic stenosis). Most patients have striking regional variations in the extent of hypertrophy in different portions of the left ventricle, and the majority demonstrate a ventricular septum whose thickness is disproportionately increased when compared with the free wall. Other patients may demonstrate symmetric hypertrophy, while others have mid-ventricular cavity obstruction or disproportionate involvement of the apex or LV free wall. In the disproportionately hypertrophied portions of the left ventricle, there is a bizarre and disorganized arrangement of myocytes, with disorganization of the myofibrillar architecture, along with a variable degree of myocardial fibrosis and thickening of the small intramural coronary arteries.

GENETIC CONSIDERATIONS About one-half of all patients with HCM have a positive family history compatible with autosomal dominant transmission. More than 400 mutations of 11 different genes that encode sarcomeric proteins have been identified; these account for ∼60% of cases.The most common are mutations of the cardiac β-myosin

heavy chain gene on chromosome 14. Others involve α-myosin heavy chains; cardiac troponins C, I, and T; cardiac myosin-binding protein C; actin; myosin light chains; and titin. Certain mutations are associated with more malignant prognoses. Many sporadic cases of HCM probably represent spontaneous mutations. Echocardiographic studies have confirmed that by the age of 20, when full expression has usually occurred, about onehalf of the first-degree relatives of patients with familial HCM have evidence of the disease. However, in many of these relatives the extent of hypertrophy is mild, no outflow tract pressure gradient is present, and symptoms are not prominent. Since the hypertrophic characteristics may not be apparent in childhood, a single normal echocardiogram in a child does not exclude the presence of the disease. Screening by echocardiography of first-degree relatives between 12 and 20 years should be carried out every 12–24 months, unless the diagnosis is established or excluded by genetic testing.

The murmur is best heard at the lower left sternal border 247 as well as at the apex, where it is often more holosystolic and blowing in quality, no doubt due to the mitral regurgitation that usually accompanies obstructive HCM.

HEMODYNAMICS

LABORATORY EVALUATION

The clinical course of HCM is highly variable. Many patients are asymptomatic or mildly symptomatic and may be relatives of patients with known disease. Unfortunately, the first clinical manifestation may be SCD, frequently occurring in children and young adults during or after physical exertion. Indeed, HCM is the most common cause of SCD in young competitive athletes. In symptomatic patients, the most common complaint is dyspnea, largely due to diastolic ventricular dysfunction, which impairs ventricular filling and leads to elevated LV diastolic, left atrial, and pulmonary capillary pressures. Other symptoms include syncope, angina pectoris, and fatigue. Symptoms are not closely related to the presence or severity of an outflow pressure gradient.

The ECG commonly shows LV hypertrophy and widespread deep, broad Q waves. The latter suggest an old myocardial infarction but actually reflect severe septal hypertrophy. Many patients demonstrate arrhythmias, both atrial (supraventricular tachycardia or atrial fibrillation) and ventricular (ventricular tachycardia), during ambulatory (Holter) monitoring. Chest roentgenography may be normal, although a mild to moderate increase in the cardiac silhouette is common. The mainstay of the diagnosis of HCM is the echocardiogram, which demonstrates LV hypertrophy, often with the septum ≥1.3 times the thickness of the posterior LV free wall. The septum may demonstrate an unusual “ground-glass” appearance, probably related to its myocardial fibrosis. SAM of the mitral valve, often accompanied by mitral regurgitation, is found in patients with pressure gradients. The LV cavity typically is small in HCM, with vigorous motion of the posterior wall but with reduced septal excursion. An uncommon form of cardiomyopathy, characterized by apical hypertrophy, is associated with giant negative T waves on the ECG and a “spade-shaped” LV cavity; it usually has a benign clinical course. CMRI is superior to echocardiography in providing accurate

PHYSICAL EXAMINATION Most patients demonstrate a double or triple apical precordial impulse and a fourth heart sound. Those with intraventricular pressure gradients may have a rapidly rising arterial pulse. The hallmark of obstructive HCM is a systolic murmur, which is typically harsh, diamondshaped, and usually begins well after the first heart sound.

Cardiomyopathy and Myocarditis

CLINICAL FEATURES

Genetic Testing

CHAPTER 21

Although not yet routinely available, genetic testing may allow a definitive diagnosis of HCM with a genetic cause to be established by identifying a mutation in a gene encoding a sarcomeric protein. Genetic testing can identify family members who are at risk for developing HCM and who, therefore, require echocardiographic screening and follow-up. It can also exclude the disease in family members.

In contrast to the obstruction produced by a fixed narrowed orifice, such as valvular aortic stenosis, the pressure gradient in HCM, when present, is dynamic and may change between examinations and even from beat to beat. Obstruction appears to result from narrowing of the LV outflow tract by systolic anterior movement (SAM) of the mitral valve against the hypertrophied septum. Three basic mechanisms are involved in the production and intensification of the dynamic intraventricular obstruction: (1) increased LV contractility; (2) decreased ventricular preload; and (3) decreased aortic impedance and pressure (afterload). Interventions that increase myocardial contractility, such as exercise and sympathomimetic amines, and those that reduce ventricular preload, such as the strain phase of the Valsalva maneuver, sudden standing, or nitroglycerin, reduce LV end-diastolic volume and, thereby, may cause an increase in the gradient and the murmur. Conversely, elevation of arterial pressure by squatting, sustained handgrip, augmentation of venous return by passive leg raising, and expansion of the blood volume (as during pregnancy) all increase ventricular volume and ameliorate the gradient and murmur.

248 measurements of regional hypertrophy and in identifying sites of regional fibrosis. Although cardiac catheterization is not required to diagnose HCM, the two typical hemodynamic features are an elevated LV diastolic pressure due to diminished compliance and, in some patients, a systolic pressure gradient, usually between the body of the left ventricle and the subaortic region. When a gradient is not present, it can be induced in some patients by provocative maneuvers, such as infusion of isoproterenol, inhalation of amyl nitrite, the Valsalva maneuver, or a premature ventricular contraction.

Treatment: HYPERTROPHIC CARDIOMYOPATHY

SECTION IV Disorders of the Heart

Because SCD often occurs during or just after physical exertion, competitive sports and very strenuous activities should be proscribed. Dehydration should be avoided, and diuretics used with caution. β-Adrenergic blockers ameliorate angina pectoris and syncope in one-third to one-half of patients. Although resting intraventricular pressure gradients are usually unchanged, these drugs may limit the increase in the gradient that occurs during exercise. It does not appear that β-adrenergic blockers offer any protection against SCD. Amiodarone appears to be effective in reducing the frequency of supraventricular as well as of life-threatening ventricular arrhythmias, and anecdotal data suggest that it may reduce the risk of SCD. Nondihydropyridine calcium channel blockers (verapamil and diltiazem) may reduce the stiffness of the left ventricle, reduce the elevated diastolic pressures, increase exercise tolerance, and, in some instances, reduce the severity of outflow tract pressure gradients. Disopyramide has been used in some patients to reduce LV contractility and the outflow pressure gradient; it may reduce symptoms as well. Digitalis, diuretics, nitrates, dihydropyridine calcium blockers, vasodilators, and β-adrenergic agonists are best avoided, particularly in patients with known LV outflow tract pressure gradients. Alcohol ingestion may produce sufficient vasodilatation to exacerbate an outflow pressure gradient. Atrial fibrillation is poorly tolerated, and a strong effort should be made to restore and then maintain sinus rhythm. Slowing of the heart rate with a β-adrenergic blocker or ablation of the AV node and insertion of a pacemaker may be indicated when sinus rhythm cannot be sustained. Surgical myotomy/myectomy of the hypertrophied septum usually abolishes intraventricular obstruction and provides lasting symptomatic improvement in about three-quarters of severely symptomatic patients with large pressure gradients who are unresponsive to

medical management. Infarction of the interventricular septum induced by ethanol injections into the septal artery (alcohol septal ablation) can also reduce obstruction and improve symptoms. However, it should be carried out only by experts. The insertion of an ICD should be considered in patients with a high-risk profile for SCD (see later).

PROGNOSIS The natural history of HCM is variable, although many patients never exhibit any clinical manifestations. Atrial fibrillation is common late in the course of the disease; its onset often leads to the development of or an increase in symptoms. Infective endocarditis occurs in 30 mm), failure of blood pressure to rise during exercise, a family history of SCD, and certain genetic mutations.

INHERITED METABOLIC CARDIOMYOPATHIES WITH LEFT VENTRICULAR HYPERTROPHY Cardiac Danon Disease This condition is caused by mutations in an X-linked lysosome-associated membrane protein (LAMP2). It is characterized by enlarged ventricular myocytes with periodic acid Schiff (PAS)–positive inclusions. Patients present in childhood with CHF and serious arrhythmias. The ECG shows severe LV hypertrophy and ventricular preexcitation. Glycogen Storage Cardiomyopathy This recently characterized condition is caused by a mutation in the γ2 regulatory subunit (PRKAG2) of adenosine monophosphate–activated protein kinase (AMPK). It is characterized by ventricular hypertrophy resembling that

observed in hypertrophic cardiomyopathies and enlarged myocytes with vacuoles in the myocytes that stain for glycogen. Fabry Disease This X-linked recessive lysosomal storage disorder is caused by deficiency of lysosomal α-galactoside A and can lead to the accumulation of glycosphingolipids in the heart, with ventricular hypertrophy resembling HCM. Because of severe impairment in ventricular filling, it is sometimes classified as a restrictive cardiomyopathy (see later). It may be associated with AV conduction abnormalities and ventricular tachyarrhythmias. CMRI is helpful in establishing the diagnosis. Treatment consists of enzyme replacement therapy with agalsidase β. Friedreich’s Ataxia

The hallmark of the restrictive cardiomyopathies (RCMs) is abnormal diastolic function (Chap. 1); the ventricular walls are excessively rigid and impede ventricular filling. In late stages systolic function is also impaired. Myocardial fibrosis, hypertrophy, or infiltration due to a variety of causes is responsible. Myocardial involvement with amyloid is a common cause of secondary restrictive cardiomyopathy, although restriction is also seen in the transplanted heart, in hemochromatosis, glycogen deposition, endomyocardial fibrosis, sarcoidosis, hypereosinophilic disease, and scleroderma; following mediastinal irradiation; and in neoplastic infiltration and myocardial fibrosis of diverse causes. In many of these conditions, particularly those with substantial concomitant endocardial involvement, partial obliteration of the ventricular cavity by fibrous tissue and thrombus contributes to the abnormally increased resistance to ventricular filling. Thromboembolic complications are frequent in such patients.

CLINICAL FEATURES The inability of the ventricles to fill limits cardiac output and raises filling pressures; thus, exercise intolerance

In patients with infiltrative cardiomyopathies, the ECG often shows low-voltage, nonspecific ST-T-wave abnormalities and various arrhythmias. Pericardial calcification on x-ray, which occurs in constrictive pericarditis, is absent. Echocardiography, CTI, and cardiac MRI typically reveal symmetrically thickened LV walls and normal or slightly reduced ventricular volumes and systolic function; the atria are usually dilated. Doppler echocardiography typically shows diastolic dysfunction. Cardiac catheterization shows a reduced cardiac output, elevation of the RV and LV end-diastolic pressures, and a dip-and-plateau configuration of the diastolic portion of the ventricular pressure pulses resembling constrictive pericarditis. Differentiation of RCM from constrictive pericarditis (Chap. 22) is of importance because the latter is often curable by surgery. Helpful in the differentiation of these two conditions are RV transvenous endomyocardial biopsy (by revealing myocardial infiltration or fibrosis in RCM) and CTI or CMRI (by demonstrating a thickened pericardium in constrictive pericarditis but not in RCM).

Treatment: RESTRICTIVE CARDIOMYOPATHY

Management is usually disappointing, except for hemochromatosis (see later) and Fabry’s disease (see earlier). Chronic anticoagulation is often recommended to reduce the risk of embolization from the heart.

EOSINOPHILIC ENDOMYOCARDIAL DISEASE Also called Loeffler’s endocarditis and fibroplastic endocarditis, this condition occurs in temperate climates. It appears to be a subcategory of the hypereosinophilic syndrome in which the heart is predominantly involved, with cardiac damage the apparent result of the toxic effects of eosinophilic proteins. Typically, the endocardium of

Cardiomyopathy and Myocarditis

RESTRICTIVE CARDIOMYOPATHY

LABORATORY EXAMINATIONS

CHAPTER 21

This is an autosomal recessive spinocerebellar degenerative disease caused by inadequate levels of frataxin, a protein involved in mitochondrial iron metabolism. Approximately one-half of the patients develop cardiac symptoms.The ECG most commonly demonstrates STsegment and T-wave abnormalities. Echocardiography and other imaging studies (CTI, CMRI) usually show symmetric LV hypertrophy or asymmetric hypertrophy of the interventricular septum compared with the free wall. Although the gross morphologic appearance of the heart in Friedreich’s ataxia may be similar to that in HCM (see earlier), cellular disarray is lacking.

and dyspnea are usually prominent. As a result of persis- 249 tently elevated systemic venous pressure, these patients commonly have dependent edema, ascites, and an enlarged, tender, and often pulsatile liver.The jugular venous pressure is elevated and does not fall normally (or may rise) with inspiration (Kussmaul’s sign).The heart sounds may be distant, and third and fourth heart sounds are common. In contrast to constrictive pericarditis (Chap. 22), which RCM resembles in many respects, the apex impulse is usually easily palpable, and mitral regurgitation is more common.

250 either or both ventricles is thickened markedly, with involvement of the underlying myocardium. Cardiac imaging typically reveals ventricular thickening, especially of the posterobasal LV wall. Mitral regurgitation is frequently present on Doppler echocardiography. Large mural thrombi may develop in either ventricle, thereby compromising the size of the ventricular cavity and serving as a source of pulmonary and systemic emboli. Hepatosplenomegaly and localized eosinophilic infiltration of other organs are usually present. Management usually includes diuretics, afterload-reducing agents, and anticoagulation. The use of glucocorticoids and hydroxyurea appears to improve survival. Surgical treatment with resection of fibrotic tissue and mitral valve repair or replacement may be helpful in selected patients.

CARDIAC AMYLOIDOSIS

SECTION IV Disorders of the Heart

Involvement of the heart is the most frequent cause of death in primary amyloidosis (AL) and hereditary amyloidosis (ATTR), with deposition of amyloid in the cardiac interstitium. On gross pathologic examination, the heart is firm, rubbery, and noncompliant and has a waxy appearance. Clinically significant cardiac involvement is uncommon in the secondary form. Focal deposits of amyloid in the hearts of elderly persons (senile cardiac amyloidosis), although common, are usually clinically insignificant. Four clinical presentations (alone or in combination) are seen: (1) diastolic dysfunction, (2) systolic dysfunction, (3) arrhythmias and conduction disturbances, and (4) orthostatic hypotension. The two-dimensional echocardiogram may be helpful in establishing the diagnosis of amyloidosis and may show a thickened myocardial wall with a diffuse, hyperrefractile “speckled” appearance. Cardiac MRI typically shows late gadolinium enhancement of the subendocardium. Aspiration of abdominal fat or biopsy of the myocardium or other organs permits the ante mortem diagnosis to be established in over threequarters of cases. Chemotherapy, often with alkylating agents such as melphalan, together with glucocorticoids, appears to have improved survival in individual cases. Heart transplantation (often combined with bone marrow transplantation or liver or kidney transplantation for hereditary amyloidosis) may help selected patients. However, the overall prognosis is poor, especially in the primary form with advanced cardiac involvement.

OTHER RESTRICTIVE CARDIOMYOPATHIES Iron-overload cardiomyopathy (hemochromatosis) is often the result of multiple transfusions or a hemoglobinopathy, most frequently β-thalassemia; the familial (autosomal recessive) form should be suspected if cardiomyopathy occurs in the presence of diabetes mellitus, hepatic

cirrhosis, and increased skin pigmentation.The diagnosis may be confirmed by endomyocardial biopsy. Cardiac ∗ MRI shows a reduced T2 signal as iron levels rise. Phlebotomy may be of some benefit if employed early in the course of the disease. Continuous subcutaneous administration of deferoxamine or other iron chelators may reduce body iron stores and result in clinical improvement. Myocardial sarcoidosis is generally associated with other manifestations of systemic disease. It may cause restrictive as well as congestive features, since cardiac infiltration by sarcoid granulomas results not only in increased stiffness of the myocardium but also in diminished systolic contractile function. A variety of arrhythmias, including high-grade AV block, have been noted. A common cardiac manifestation of systemic sarcoidosis is RV overload due to pulmonary hypertension as a result of parenchymal pulmonary involvement. Many patients are treated empirically with glucocorticoids. The carcinoid syndrome (Chap. 20) results in endocardial fibrosis and stenosis and/or regurgitation of the tricuspid and/or pulmonary valve; morphologically similar lesions have been seen with the use of the anorexic agents fenfluramine and phentermine.

MYOCARDITIS Myocarditis, i.e., cardiac inflammation, is most commonly the result of an infectious process, frequently complicated by autoimmunity. Myocarditis may also result from hypersensitivity to drugs (most commonly tricyclic antidepressants, antibiotics, and antipsychotics) or it may be caused by irradiation, chemicals, or physical agents.While almost every infective agent is capable of producing myocarditis (Table 21-1), clinically significant acute myocarditis in the United States is caused most commonly by viruses, especially Coxsackievirus B, adenovirus, hepatitis C virus, and HIV. Symptomatic viral myocarditis may be secondary to continued viral replication and/or autoimmune activation following viral infection.

CLINICAL FEATURES Patients with viral myocarditis may give a history of a preceding upper respiratory febrile illness or a flulike syndrome, and viral nasopharyngitis or tonsillitis may be evident.The clinical spectrum ranges from an asymptomatic state, with the presence of myocarditis inferred only by the finding of transient electrocardiographic ST-T-wave abnormalities, to a fulminant condition with arrhythmias, acute CHF, and early death. In some patients, myocarditis simulates an acute coronary syndrome (Chap. 34), with chest pain, ECG changes, and elevated serum levels of troponin, but it typically occurs in patients younger than those with coronary atherosclerosis. The physical examination is often normal, although more severe cases may show a muffled first heart sound,

along with a third heart sound and a murmur of mitral regurgitation. A pericardial friction rub may be audible in patients with associated pericarditis. The isolation of virus from the stool, pharyngeal washings, or other body fluids and changes in specific antibody titers may be helpful clinically. Endomyocardial biopsy, carried out early in the illness, may show round-cell infiltration and necrosis of adjacent myocytes. CMRI frequently exhibits contrast enhancement (Chap. 12) and is valuable in identifying sites likely to exhibit typical histologic changes on biopsy, as well as in monitoring the activity of the disease. Although viral myocarditis is most often self-limited and without sequelae, severe involvement may recur.Acute viral myocarditis, especially when accompanied by severe LV dysfunction (LVEF 30 U/L) strongly supports the diagnosis of tuberculous pericarditis.

agent. Commonly, there is an antecedent infection of 259 the respiratory tract, but in many patients such an association is not evident, and viral isolation and serologic studies are negative. Pericardial effusion is a common cardiac manifestation of HIV; it is usually secondary to infection (often mycobacterial) or neoplasm, most frequently lymphoma. In full-blown AIDS, pericardial effusion is associated with a shortened survival. Most frequently, a viral causation cannot be established; the term idiopathic acute pericarditis is then appropriate.Viral or idiopathic acute pericarditis occurs at all ages but is more frequent in young adults, and is often associated with pleural effusions and pneumonitis. The almost simultaneous development of fever and precordial pain, often 10–12 days after a presumed viral illness, constitutes an important feature in the differentiation of acute pericarditis from AMI, in which pain precedes fever. The constitutional symptoms are usually mild to moderate, and a pericardial friction rub is often audible. The disease ordinarily runs its course in a few days to 4 weeks.The ST-segment alterations in the ECG usually disappear after 1 or more weeks, but the abnormal T waves may persist for several years and be a source of confusion in persons without a clear history of pericarditis. Pleuritis and pneumonitis frequently accompany pericarditis. Accumulation of some pericardial fluid is common, and both tamponade and constrictive pericarditis are possible complications. Recurrent (relapsing) pericarditis occurs in about one-fourth of patients with acute idiopathic pericarditis. In a smaller number, there are multiple recurrences.

260

After the patient has been asymptomatic and afebrile for about a week, the dose of the NSAID may be tapered gradually. Colchicine may prevent recurrences, but when recurrences are multiple, frequent, disabling, continue beyond 2 years, and are not controlled by pulses of high doses of glucocorticoids, pericardiectomy may be carried out in an attempt to terminate the illness.

Post-cardiac Injury Syndrome

SECTION IV Disorders of the Heart

Acute pericarditis may appear under a variety of circumstances that have one common feature: previous injury to the myocardium with blood in the pericardial cavity.The syndrome may develop after a cardiac surgery (postpericardiotomy syndrome); after cardiac trauma, blunt or penetrating (Chap. 23); or after perforation of the heart with a catheter. Rarely, it follows AMI. The clinical picture mimics acute viral or idiopathic pericarditis. The principal symptom is the pain of acute pericarditis, which usually develops 1–4 weeks following the cardiac injury (1–3 days following AMI) but sometimes appears only after an interval of months. Recurrences are common and may occur up to 2 years or more after the injury. Fever with temperature up to 40°C, pericarditis, pleuritis, and pneumonitis are the outstanding features, and the bout of illness usually subsides in 1 or 2 weeks. The pericarditis may be of the fibrinous variety or it may be a pericardial effusion, which is often serosanguineous, but rarely causes tamponade. Leukocytosis, an increased sedimentation rate, and electrocardiographic changes typical of acute pericarditis may also occur. The mechanisms responsible for this syndrome have not been identified, but they are probably the result of a hypersensitivity reaction to antigen which originates from injured myocardial tissue and/or pericardium. Circulating myocardial antisarcolemmal and antifibrillar autoantibodies occur frequently, but their precise role has not been defined. Viral infection may also play an etiologic role, since antiviral antibodies are often elevated in patients who develop this syndrome following cardiac surgery. Often no treatment is necessary aside from aspirin and analgesics. The management of pericardial effusion and tamponade is discussed above. When the illness is followed by a series of disabling recurrences, therapy with an NSAID, colchicine, or a glucocorticoid is usually effective.

DIFFERENTIAL DIAGNOSIS Because there is no specific test for acute idiopathic pericarditis, the diagnosis is one of exclusion. Consequently, all other disorders that may be associated with acute fibrinous pericarditis must be considered. A common

diagnostic error is mistaking acute viral or idiopathic pericarditis for AMI and vice versa. When acute fibrinous pericarditis is associated with AMI (Chap. 35), it is characterized by fever, pain, and a friction rub in the first 4 days following the development of the infarct. ECG abnormalities (such as the appearance of Q waves, brief ST-segment elevations with reciprocal changes, and earlier T-wave changes in AMI) and the extent of the elevations of myocardial enzymes are helpful in differentiating pericarditis from AMI. Pericarditis secondary to post-cardiac injury is differentiated from acute idiopathic pericarditis chiefly by timing. If it occurs within a few days or weeks of an AMI, a chest blow, a cardiac perforation, or cardiac operation, it may be justified to conclude that the two are probably related. If the infarct has been silent or the chest blow forgotten, the relationship to the pericarditis may not be recognized. It is important to distinguish pericarditis due to collagen vascular disease from acute idiopathic pericarditis. Most important in the differential diagnosis is the pericarditis due to systemic lupus erythematosus (SLE) or druginduced (procainamide or hydralazine) lupus. Pain is often present in pericarditis due to collagen vascular disease. Sometimes in SLE the pericarditis appears as an asymptomatic effusion and, rarely, tamponade develops. When pericarditis occurs in the absence of any obvious underlying disorder, the diagnosis of SLE may be suggested by a rise in the titer of antinuclear antibodies. Acute pericarditis is an occasional complication of rheumatoid arthritis, scleroderma, and polyarteritis nodosa, and other evidence of these diseases is usually obvious. Asymptomatic pericardial effusion is also frequent in these disorders. It is important to question every patient with acute pericarditis about the ingestion of procainamide, hydralazine, isoniazid, cromolyn, and minoxidil, since these drugs can cause this syndrome.The pericarditis of acute rheumatic fever is generally associated with evidence of severe pancarditis and with cardiac murmurs (Chap. 26). Pyogenic (purulent) pericarditis is usually secondary to cardiothoracic operations, by extension of infection from the lungs or pleural cavities, from rupture of the esophagus into the pericardial sac, or rupture of a ring abscess in a patient with infective endocarditis, or can occur if septicemia complicates aseptic pericarditis. It is accompanied by fever, chills, septicemia, and evidence of infection elsewhere and generally has a poor prognosis. The diagnosis is made by examination of the pericardial fluid. Acute pericarditis may also complicate the viral, pyogenic, mycobacterial, and fungal infections that occur with HIV infection. Pericarditis of renal failure occurs in up to one-third of patients with chronic uremia (uremic pericarditis), is also seen in patients undergoing chronic dialysis with normal levels of blood urea and creatinine, and is termed dialysisassociated pericarditis. These two forms of pericarditis

may be fibrinous and are generally associated with an effusion that may be sanguineous. A friction rub is common, but pain is usually absent or mild. Treatment with an NSAID and intensification of dialysis are usually adequate. Occasionally, tamponade occurs and pericardiocentesis is required.When the pericarditis of renal failure is recurrent or persistent, a pericardial window should be created or pericardiectomy may be necessary. Pericarditis due to neoplastic diseases results from extension or invasion of metastatic tumors (most commonly carcinoma of the lung and breast, malignant melanoma, lymphoma, and leukemia) to the pericardium; pain, atrial arrhythmias, and tamponade are complications that occur occasionally. Diagnosis is made by pericardial fluid cytology or pericardial biopsy. Mediastinal irradiation for neoplasm may cause acute pericarditis and/or chronic constrictive pericarditis after eradication of the tumor. Unusual causes of acute pericarditis include syphilis, fungal infection (histoplasmosis, blastomycosis, aspergillosis, and candidiasis), and parasitic infestation (amebiasis, toxoplasmosis, echinococcosis, trichinosis).

CHRONIC PERICARDIAL EFFUSIONS

Myxedema may be responsible for chronic pericardial effusion that is sometimes massive but rarely, if ever, causes cardiac tamponade. The cardiac silhouette is markedly enlarged, and an echocardiogram distinguishes cardiomegaly from pericardial effusion. The diagnosis of myxedema can be confirmed by tests for thyroid function. Myxedematous pericardial effusion responds to thyroid hormone replacement. Neoplasms, SLE, rheumatoid arthritis, mycotic infections, radiation therapy to the chest, pyogenic infections, and chylopericardium may also cause chronic pericardial effusion and should be considered and specifically sought in such patients. Aspiration and analysis of the pericardial fluid are often helpful in diagnosis. Pericardial fluid should be analyzed as described earlier. Grossly sanguineous pericardial fluid results most commonly from a neoplasm, tuberculosis, renal failure, or slow leakage from an aortic aneurysm. Pericardiocentesis may resolve large effusions, but pericardiectomy may be required with recurrence. Intrapericardial instillation of sclerosing agents or antineoplastic agents (e.g., bleomycin) may be used to prevent reaccumulation of fluid.

Pericardial Disease

Other Causes

This disorder results when the healing of an acute fibrinous or serofibrinous pericarditis or the resorption of a chronic pericardial effusion is followed by obliteration of the pericardial cavity with the formation of granulation tissue. The latter gradually contracts and forms a firm scar, encasing the heart and interfering with filling of the ventricles. In developing nations where the condition is prevalent, a high percentage of cases is of tuberculous origin, but in North America this is now an infrequent cause. Chronic constrictive pericarditis may follow acute or relapsing viral or idiopathic pericarditis, trauma with organized blood clot, cardiac surgery of any type, mediastinal irradiation, purulent infection, histoplasmosis, neoplastic disease (especially breast cancer, lung cancer, and lymphoma), rheumatoid arthritis, SLE, and chronic renal failure with uremia treated by chronic dialysis. In many patients the cause of the pericardial disease is undetermined, and in them an asymptomatic or forgotten bout of viral pericarditis, acute or idiopathic, may have been the inciting event. The basic physiologic abnormality in patients with chronic constrictive pericarditis is the inability of the ventricles to fill because of the limitations imposed by the rigid, thickened pericardium or the tense pericardial fluid. In constrictive pericarditis, ventricular filling is unimpeded during early diastole but it is reduced abruptly when the elastic limit of the pericardium is reached, while in cardiac tamponade, ventricular filling is impeded throughout diastole. In both conditions, ventricular end-diastolic and stroke volumes are reduced and the end-diastolic pressures in both ventricles and the mean pressures in the atria, pulmonary veins, and systemic veins are all elevated to similar levels, i.e., within 5 mmHg of one another. Despite these hemodynamic changes, myocardial function may be normal or only slightly impaired in chronic constrictive pericarditis. However, the fibrotic process may extend into the myocardium and cause myocardial scarring, and atrophy, and venous congestion may then be due to the combined effects of the pericardial and myocardial lesions. In constrictive pericarditis, the right and left atrial pressure pulses display an M-shaped contour, with prominent x and y descents; the y descent, which is absent or diminished in cardiac tamponade, is the most prominent deflection in constrictive pericarditis; it reflects rapid early filling of the ventricles.The y descent is interrupted by a rapid rise in atrial pressure during early diastole, when ventricular filling is impeded by the constricting pericardium. These characteristic changes are transmitted to the jugular veins, where they may be recognized by inspection. In constrictive pericarditis, the ventricular pressure pulses in both ventricles exhibit characteristic

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CHAPTER 22

Chronic pericardial effusions are sometimes encountered in patients without an antecedent history of acute pericarditis. They may cause few symptoms per se, and their presence may be detected by finding an enlarged cardiac silhouette on chest roentgenogram.Tuberculosis is a common cause.

CHRONIC CONSTRICTIVE PERICARDITIS

262 “square root” signs during diastole.These hemodynamic changes, although characteristic, are not pathognomonic of constrictive pericarditis and may also be observed in cardiomyopathies characterized by restriction of ventricular filling (Chap. 21) (Table 22-2).

CLINICAL AND LABORATORY FINDINGS

SECTION IV Disorders of the Heart

Weakness, fatigue, weight gain, increased abdominal girth, abdominal discomfort, a protuberant abdomen, and edema are common. The patient often appears chronically ill, and in advanced cases there are anasarca, skeletal muscle wasting, and cachexia. Exertional dyspnea is common, and orthopnea may occur, although it is usually not severe. Acute left ventricular failure (acute pulmonary edema) is very uncommon.The cervical veins are distended and may remain so even after intensive diuretic treatment, and venous pressure may fail to decline during inspiration (Kussmaul’s sign).The latter is frequent in chronic pericarditis but may also occur in tricuspid stenosis, right ventricular infarction, and restrictive cardiomyopathy. The pulse pressure is normal or reduced. In about one-third of the cases, a paradoxical pulse (p. 257) can be detected. Congestive hepatomegaly is pronounced and may impair hepatic function and cause jaundice; ascites is common and is usually more prominent than dependent edema. The apical pulse is reduced and may retract in systole (Broadbent’s sign). The heart sounds may be distant; an early third heart sound, i.e., a pericardial knock, occurring 0.09–0.12 s after aortic valve closure at the cardiac apex, is often conspicuous; it occurs with the abrupt cessation of ventricular filling. A systolic murmur of tricuspid regurgitation may be present. The ECG frequently displays low voltage of the QRS complexes and diffuse flattening or inversion of the T waves. Atrial fibrillation is present in about one-third of patients. The chest roentgenogram shows a normal or slightly enlarged heart; pericardial calcification is most common in tuberculous pericarditis. Inasmuch as the usual physical signs of cardiac disease (murmurs, cardiac enlargement) may be inconspicuous or absent in chronic constrictive pericarditis, hepatic enlargement and dysfunction associated with jaundice and intractable ascites may lead to a mistaken diagnosis of hepatic cirrhosis. This error can be avoided if the neck veins are inspected carefully in patients with ascites and hepatomegaly. Given a clinical picture resembling hepatic cirrhosis, but with the added feature of distended neck veins, careful search for thickening of the pericardium by CT (Fig. 12-8) or MRI should be carried out and may disclose this curable or remediable form of heart disease. The two-dimensional transthoracic echocardiogram typically shows pericardial thickening, dilatation of the inferior vena cava and hepatic veins, and a sharp halt in

ventricular filling in early diastole, with normal ventricular systolic function and flattening of the left ventricular posterior wall. Atrial enlargement may be seen, especially in patients with long-standing constrictive physiology. There is a distinctive pattern of transvalvular flow velocity on Doppler flow-velocity echocardiography. During inspiration there is an exaggerated reduction in blood flow velocity in the pulmonary veins and across the mitral valve and a leftward shift of the ventricular septum; the opposite occurs during expiration. Diastolic flow velocity in the vena cavae into the right atrium and across the tricuspid valve increases in an exaggerated manner during inspiration and declines during expiration (Fig. 22-5). However, echocardiography cannot definitively exclude the diagnosis of constrictive pericarditis. MRI and CT scanning (Fig. 22-6) are more accurate than echocardiography in establishing or excluding the presence of a thickened pericardium. Pericardial thickening and even pericardial calcification, however, are not synonymous with constrictive pericarditis since they may occur without seriously impairing ventricular filling.

DIFFERENTIAL DIAGNOSIS Like chronic constrictive pericarditis, cor pulmonale (Chap. 17) may be associated with severe systemic venous hypertension but little pulmonary congestion; the heart is usually not enlarged, and a paradoxical pulse may be present. However, in cor pulmonale, advanced parenchymal pulmonary disease is usually obvious and venous pressure falls during inspiration, i.e., Kussmaul’s sign is negative. Tricuspid stenosis (Chap. 20) may also simulate chronic constrictive pericarditis; congestive hepatomegaly,

FIGURE 22-5 Constrictive pericarditis Doppler schema of respirophasic changes in mitral and tricuspid inflow. Reciprocal patterns of ventricular filling are assessed on pulsed Doppler examination of mitral (MV) and tricuspid (TV) inflow. (Courtesy of Bernard E. Bulwer, MD; with permission.)

263

FIGURE 22-6 Cardiovascular magnetic resonance in a patient with constrictive pericarditis. On the right is a basal short-axis view of the ventricles showing a thickened pericardium encasing the heart (arrows). On the left is a transaxial view, again showing the thickened pericardium, particularly over

Treatment: CONSTRICTIVE PERICARDITIS

Subacute Effusive-Constrictive Pericarditis This form of pericardial disease is characterized by the combination of a tense effusion in the pericardial space and constriction of the heart by thickened pericardium. It shares a number of features both with chronic pericardial effusion producing cardiac compression and with pericardial constriction. It may be caused by tuberculosis (see later), multiple attacks of acute idiopathic pericarditis, radiation, traumatic pericarditis, renal failure, scleroderma, and neoplasms. The heart is generally enlarged, and a paradoxical pulse and a prominent x descent (without a prominent y descent) are present in

Pericardial Disease

Pericardial resection is the only definitive treatment of constrictive pericarditis, but dietary sodium restriction and diuretics are useful during preoperative preparation. Coronary arteriography should be carried out preoperatively in patients older than 50 years to exclude unsuspected coronary disease. The benefits derived from cardiac decortication are usually progressive over a period of months. The risk of this operation depends on the extent of penetration of the myocardium by the calcific process, by the severity of myocardial atrophy, by the extent of secondary impairment of hepatic and/or renal function, and by the patient’s general condition. Operative mortality is in the range of 5–10%; the patients with the most severe disease are at highest risk. Therefore, surgical treatment should be carried out relatively early in the course.

CHAPTER 22

splenomegaly, ascites, and venous distention may be equally prominent. However, in tricuspid stenosis, a characteristic murmur as well as the murmur of accompanying mitral stenosis are usually present. In tricuspid stenosis, a paradoxical pulse and a steep, deep y descent in the jugular venous pulse do not occur, serving to differentiate it from chronic constrictive pericarditis. Because constrictive pericarditis can be corrected surgically, it is important to distinguish chronic constrictive pericarditis from restrictive cardiomyopathy (Chap. 21), which has a similar physiologic abnormality, i.e., restriction of ventricular filling. In many of these patients the ventricular wall is thickened on echocardiographic examination (Table 22-2). The features favoring the diagnosis of restrictive cardiomyopathy over chronic constrictive pericarditis include a well-defined apex beat, cardiac enlargement, and pronounced orthopnea with attacks of acute left ventricular failure, left ventricular hypertrophy, gallop sounds (in place of a pericardial knock), bundle branch block, and in some cases abnormal Q waves on the ECG. The typical echocardiographic features of constrictive pericarditis (see earlier) are useful in the differential diagnosis in chronic constrictive pericarditis (Fig. 22-5). CT scanning (usually with contrast) and MRI are key in distinguishing between restrictive cardiomyopathy and chronic constrictive pericarditis. In the former, the ventricular walls are hypertrophied, while in the latter the pericardium is thickened and sometimes calcified. When a patient has progressive, disabling, and unresponsive congestive heart failure and displays any of the features of constrictive heart disease, Doppler echocardiography to record respiratory effects on transvalvular flow, and an MRI or CT scan should be obtained to detect or exclude constrictive pericarditis, since the latter is usually curable.

the right heart, but also a pleural effusion (Pl Eff). LV, left ventricle; RV, right ventricle. [From D Pennell: Cardiovascular magnetic resonance, in DP Zipes et al (eds): Braunwald’s Heart Disease, 7th ed. Philadelphia, Elsevier, 2005.]

264 the atrial and jugular venous pressure pulses. Following pericardiocentesis, the physiologic findings may change from those of cardiac tamponade to those of pericardial constriction, with a “square root” sign in the ventricular pressure pulse and a prominent y descent in the atrial and jugular venous pressure pulses. Furthermore, the intrapericardial pressure and the central venous pressure may decline, but not to normal. The diagnosis can be established by pericardiocentesis followed by pericardial biopsy. In many patients the condition progresses to the chronic constrictive form of the disease. Wide excision of both the visceral and parietal pericardium is usually effective therapy.

TUBERCULOUS PERICARDIAL DISEASE

SECTION IV Disorders of the Heart

This chronic infection is a common cause of chronic pericardial effusion, although less so in the United States than in Africa,Asia, the Middle East, and other parts of the developing world where active tuberculosis is endemic. The clinical picture is that of a chronic, systemic illness in a patient with pericardial effusion. It is important to consider this diagnosis in a patient with known tuberculosis, with HIV, and with fever, chest pain, weight loss, and enlargement of the cardiac silhouette of undetermined origin. Inasmuch as treatment is quite effective, overlooking a tuberculous pericardial effusion may have serious consequences. If the etiology of chronic pericardial effusion remains obscure, despite detailed analysis of the pericardial fluid (see earlier), a pericardial biopsy, preferably by a limited thoracotomy, should be performed. If definitive evidence is then still lacking but the specimen shows granulomata with caseation, antituberculous chemotherapy is indicated. If the biopsy specimen shows a thickened pericardium, pericardiectomy should be carried out to prevent the development of constriction, a serious complication of tuberculosis that occurs in about one-half of patients with tuberculous pericardial effusion despite treatment with chemotherapy and glucocorticoids.Tubercular cardiac constriction should be treated surgically while the patient is receiving antituberculous chemotherapy. In many patients, subacute effusive-constrictive pericarditis develops.

OTHER DISORDERS OF THE PERICARDIUM Pericardial cysts appear as rounded or lobulated deformities of the cardiac silhouette, most commonly at the right cardiophrenic angle.They do not cause symptoms, and their major clinical significance lies in the possibility of confusion with a tumor, ventricular aneurysm, or massive cardiomegaly. Tumors involving the pericardium are most commonly secondary to malignant neoplasms originating in or invading the mediastinum, including carcinoma of the bronchus and breast, lymphoma, and melanoma. The most common primary malignant tumor is the mesothelioma. The usual clinical picture of malignant pericardial tumor is an insidiously developing, often bloody, pericardial effusion. Surgical exploration is required to establish a definitive diagnosis and to carry out definitive or, more commonly, palliative treatment. FURTHER READINGS AXEL L: Assessment of pericardial disease by magnetic resonance and computed tomography. J Magn Reson Imaging 19:816, 2004 HOIT BD: Management of effusive and constrictive pericardial heart disease. Circulation 105:2939, 2002 IMAZIO M et al: Diagnosis an management of pericardial diseases. Nat Rev Cardiol 6:743, 2009 LANGE RA, HILLIS LD: Acute pericarditis. N Engl J Med 351:2195, 2004 LEWINTER M, KABBANI S: Pericardial diseases, in Braunwald’s Heart Disease, 8th ed, P. Libby et al (eds). Philadelphia, Saunders, 2008 MAISCH B et al: Guidelines on the diagnosis and management of pericardial diseases executive summary: the Task Force on the Diagnosis and Management of Pericardial Diseases of the European Society of Cardiology. Eur Heart J 25:587, 2004 MAYOSI BM et al: Tuberculous pericarditis. Circulation 112:3608, 2005 ———: Contemporary trends in the epidemiology and management of cardiomyopathy and pericarditis in Sub-Saharan Africa. Heart 93:1176, 2007 RAJAGOPALAN N et al: Comparison of new Doppler echocardiographic methods to differentiate constrictive pericardial heart disease and restrictive cardiomyopathy. Am J Cardiol 87:86, 2001

CHAPTER 23

TUMORS AND TRAUMA OF THE HEART Eric H. Awtry

■

Wilson S. Colucci

■ Tumors of the Heart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 Primary Tumors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 265 Tumors Metastatic to the Heart . . . . . . . . . . . . . . . . . . . . . . . 267 ■ Traumatic Cardiac Injury . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269

all ages, most commonly in the third through sixth decades, with a female predilection. Approximately 90% of myxomas are sporadic; the remainder are familial with autosomal dominant transmission. The familial variety often occurs as part of a syndrome complex (Carney complex) that comprises (1) myxomas (cardiac, skin, and/or breast), (2) lentigines and/or pigmented nevi, and (3) endocrine overactivity (primary nodular adrenal cortical disease with or without Cushing’s syndrome, testicular tumors, and/or pituitary adenomas with gigantism or acromegaly). Certain constellations of findings have been referred to as the NAME syndrome (nevi, atrial myxoma, myxoid neurofibroma, and ephelides) or the LAMB syndrome (lentigines, atrial myxoma, and blue nevi), although these likely represent subsets of the Carney complex.The genetic basis of this complex has not been completely elucidated; however, patients frequently have mutations in the tumor-suppressor gene PRKAR1A, which encodes the protein kinase A type I-α regulatory subunit. Pathologically, myxomas are gelatinous structures consisting of myxoma cells embedded in a stroma rich in glycosaminoglycans. Most are pedunculated on a fibrovascular stalk and average 4–8 cm in diameter. Most are solitary and located in the atria, particularly the left atrium, where they usually arise from the interatrial septum in the vicinity of the fossa ovalis. In contrast to sporadic tumors, familial or myxoma syndrome tumors tend to occur in younger individuals, are often multiple, may be ventricular in location, and are more likely to recur after initial resection.

TUMORS OF THE HEART PRIMARY TUMORS Primary tumors of the heart are rare. Approximately three-quarters are histologically benign, more than onehalf of which are myxomas. Malignant tumors, almost all of which are sarcomas, account for 25% of primary cardiac tumors (Table 23-1). All cardiac tumors, regardless of pathologic type, have the potential to cause lifethreatening complications. Many tumors are now curable by surgery; thus, early diagnosis is imperative. Clinical Presentation Cardiac tumors may present with a wide array of cardiac and noncardiac manifestations, which depend in large part on the location and size of the tumor. Many of the manifestations are nonspecific features of more common forms of heart disease, such as chest pain, syncope, heart failure, murmurs, arrhythmias, conduction disturbances, and pericardial effusion with or without tamponade.Additionally, embolic phenomena and constitutional symptoms may occur. Myxoma Myxomas are the most common type of primary cardiac tumor in all age groups, accounting for one-third to one-half of all cases at postmortem and for about threequarters of the tumors treated surgically. They occur at

265

266

positional in nature, owing to the effects of gravity on tumor position. A characteristic low-pitched sound, referred to as a “tumor plop,” may be appreciated on auscultation during early or mid-diastole and is thought to result from the impact of the tumor against the mitral valve or ventricular wall. Myxomas may also present with peripheral or pulmonary emboli or with constitutional signs and symptoms, including fever, weight loss, cachexia, malaise, arthralgias, rash, digital clubbing, Raynaud’s phenomenon, hypergammaglobulinemia, anemia, polycythemia, leukocytosis, elevated erythrocyte sedimentation rate, thrombocytopenia, or thrombocytosis. Not surprisingly, patients with myxomas are frequently misdiagnosed as having endocarditis, collagen vascular disease, or a paraneoplastic syndrome. Two-dimensional transthoracic or omniplane transesophageal echocardiography is useful in the diagnosis of cardiac myxoma and allows assessment of tumor size and determination of the site of tumor attachment, both important considerations in the planning of surgical excision (Fig. 23-1). CT and MRI may provide important information regarding size, shape, composition, and surface characteristics of the tumor (Fig. 23-2). Although cardiac catheterization and angiography were previously performed routinely prior to tumor resection, they are no longer considered mandatory when adequate noninvasive information is available and other cardiac disorders (e.g., coronary artery disease) are not considered likely. Additionally, catheterization of the chamber from which the tumor arises carries the risk of tumor embolization. Because myxomas may be familial, echocardiographic screening of first-degree relatives is appropriate, particularly if the patient is young and has multiple tumors or evidence of myxoma syndrome.

TABLE 23-1 RELATIVE INCIDENCE OF PRIMARY TUMORS OF THE HEART TYPE

Benign Myxoma Rhabdomyoma Fibroma Hemangioma Atrioventricular nodal Granular cell Lipoma Paraganglioma Myocytic hamartoma Histiocytoid cardiomyopathy Inflammatory pseudotumor Other benign tumors Malignant Sarcoma Lymphoma

NUMBER

PERCENT

199 114 20 20 17 10 4 2 2 2 2 2 4 144 137 7

58.0 33.2 5.8 5.8 5.0 2.9 1.2 0.6 0.6 0.6 0.6 0.6 1.2 42.0 39.9 2.1

Source: Modified from A Burke, R Virmani: Atlas of Tumor Pathology. Tumors of the Heart and Great Vessels. Washington, DC, Armed Forces Institute of Pathology 1996, p. 231; with permission.

SECTION IV Disorders of the Heart

Myxomas commonly present with obstructive signs and symptoms. The most common clinical presentation mimics that of mitral valve disease—either stenosis owing to tumor prolapse into the mitral orifice or regurgitation resulting from tumor-induced valvular trauma.Ventricular myxomas may cause outflow obstruction similar to that caused by subaortic or subpulmonic stenosis. The symptoms and signs of myxoma may be sudden in onset or

A

FIGURE 23-1 Transthoracic echocardiogram demonstrating a large atrial myxoma. The myxoma (Myx) fills the entire left atrium in systole (panel A) and prolapses across the mitral valve and

B

into the left ventricle (LV) during diastole (panel B). RA, right atrium; RV, right ventricle. (Courtesy of Dr. Michael Tsang; with permission.)

failure (CHF), restrictive or hypertrophic cardiomyopathy, 267 or pericardial constriction. Rhabdomyomas are probably hamartomatous growths, are multiple in 90% of cases, and are strongly associated with tuberous sclerosis. These tumors have a tendency to regress completely or partially; only those tumors that cause obstruction require surgical resection. Fibromas are usually single, are often calcified, tend to grow and cause obstructive symptoms, and should be resected. Hemangiomas and mesotheliomas are generally small tumors, most often intramyocardial in location, and may cause atrioventricular (AV) conduction disturbances and even sudden death as a result of their propensity to develop in the region of the AV node. Other benign tumors arising from the heart include teratoma, chemodectoma, neurilemoma, granular cell myoblastoma, and bronchogenic cysts. Sarcoma FIGURE 23-2 Cardiac MRI demonstrating a rounded mass (M) within the left atrium (LA). Pathologic evaluation at the time of surgery revealed it to be an atrial myxoma. LV, left ventricle; RA, right atrium; RV, right ventricle.

Other Benign Tumors Cardiac lipomas, although relatively common, are usually incidental findings at postmortem examination; however, they may grow as large as 15 cm and may present with symptoms owing to mechanical interference with cardiac function, arrhythmias, or conduction disturbances, or as an abnormality of the cardiac silhouette on chest x-ray. Papillary fibroelastomas are the most common tumors of the cardiac valves. Although usually clinically silent, they can cause valve dysfunction and may embolize distally, resulting in transient ischemic attacks, stroke, or myocardial infarction.Therefore, these tumors should be resected even when asymptomatic. Rhabdomyomas and fibromas are the most common cardiac tumors in infants and children and usually occur in the ventricles where they may produce mechanical obstruction to blood flow, thereby mimicking valvular stenosis, congestive heart

Treatment: SARCOMA

At the time of presentation sarcomas have often spread too extensively to allow for surgical excision. Although scattered reports exist of palliation with surgery, radiotherapy, and/or chemotherapy, the response of cardiac sarcomas to these therapies is generally poor. The one exception appears to be cardiac lymphosarcomas, which may respond to a combination of chemotherapy and radiotherapy.

TUMORS METASTATIC TO THE HEART Tumors metastatic to the heart are much more common than primary tumors, and their incidence is likely to increase as the life expectancy of patients with various forms of malignant neoplasms is extended by more effective therapy. Although cardiac metastases occur in 1–20% of all tumor types, the relative incidence is especially high in malignant melanoma and, to a somewhat lesser extent, in leukemia and lymphoma. In absolute terms, the most common primary originating sites of cardiac

Tumors and Trauma of the Heart

Surgical excision utilizing cardiopulmonary bypass is indicated, regardless of tumor size, and is generally curative. Myxomas recur in ∼12–22% of familial cases but in only 1–2% of sporadic cases. Tumor recurrence is most likely due to multifocal lesions in the former and inadequate resection in the latter.

CHAPTER 23

Treatment: PRIMARY TUMOR

Almost all primary cardiac malignancies are sarcomas, which may be of several histologic types. In general, the tumors are characterized by rapid progression culminating in the patient’s death within weeks to months from the time of presentation, as a result of hemodynamic compromise, local invasion, or distant metastases. Sarcomas commonly involve the right side of the heart, are characterized by rapid growth, frequently invade the pericardial space, and may obstruct the cardiac chambers or vena cavae. Sarcomas may also occur on the left side of the heart and may be mistaken for myxomas.

268 metastases are carcinoma of the breast and lung, reflect-

SECTION IV Disorders of the Heart

ing the high incidence of these cancers. Cardiac metastases almost always occur in the setting of widespread primary disease, and most often either primary or metastatic disease exists elsewhere in the thoracic cavity. Nevertheless, cardiac metastasis may occasionally be the initial presentation of an extrathoracic tumor. Cardiac metastases may occur via hematogenous or lymphangitic spread or by direct tumor invasion.They generally manifest as small, firm nodules; diffuse infiltration may also occur, especially with sarcomas or hematologic neoplasms.The pericardium is most often involved, followed by myocardial involvement of any chamber, and, rarely, by involvement of the endocardium or cardiac valves. Cardiac metastases are clinically apparent only ∼10% of the time, are usually not the cause of the patient’s presentation, and rarely are the cause of death. The vast majority occur in the setting of a previously recognized malignant neoplasm. When symptomatic, cardiac metastases may result in a variety of clinical features, including dyspnea, acute pericarditis, cardiac tamponade, ectopic tachyarrhythmias, heart block, CHF, and rapid enlargement of the cardiac silhouette on chest x-ray. As with primary cardiac tumors, the clinical presentation reflects more the location and size of the tumor rather than its histologic type. Many of these signs and symptoms may also result from myocarditis, pericarditis, or cardiomyopathy induced by radiotherapy or chemotherapy. Electrocardiographic (ECG) findings are nonspecific. On chest x-ray, the cardiac silhouette is most often normal but may be enlarged or exhibit a bizarre contour. Echocardiography is useful for identifying pericardial effusions and for visualizing larger metastases, although CT and radionuclide imaging with gallium or thallium may more clearly define the tumor burden. Cardiac MRI offers superb image quality and plays a central role in the diagnostic evaluation of cardiac metastases and cardiac tumors in general. Pericardiocentesis may allow for a specific cytologic diagnosis in patients with malignant pericardial effusions. Angiography is rarely necessary but may delineate discrete lesions.

Treatment: TUMORS METASTATIC TO THE HEART

Most patients with cardiac metastases have advanced malignant disease; thus, therapy is generally palliative and consists of treatment of the primary tumor. Symptomatic malignant pericardial effusions should be drained by pericardiocentesis. Concomitant instillation of a sclerosing agent (e.g., tetracycline) may delay or prevent reaccumulation of the effusion, while creation of a pericardial window allows drainage of the effusion to the pleural space.

TRAUMATIC CARDIAC INJURY Traumatic cardiac injury may be caused by either penetrating or nonpenetrating trauma. Penetrating injuries most often result from gunshot or knife wounds, and the site of entry is usually obvious. Nonpenetrating injuries most often occur during motor vehicle accidents, either from a rapid deceleration injury or from impact of the chest against the steering wheel, and may be associated with significant cardiac injury even in the absence of external signs of thoracic trauma. Myocardial contusions are the most common form of nonpenetrating cardiac injury and may initially be overlooked in trauma patients as the clinical focus is directed toward other more obvious injuries. Myocardial necrosis may occur as a direct result of the blunt injury or as a result of traumatic coronary laceration or thrombosis. The contused myocardium is pathologically similar to infarcted myocardium and may be associated with atrial or ventricular arrhythmias, conduction disturbances including bundle branch block, or ECG abnormalities resembling those of infarction or pericarditis. Thus, it is important to consider contusion as a cause of otherwise unexplained ECG changes in a trauma patient. Serum creatine kinase (CK-MB) isoenzyme levels are increased in ∼20% of patients suffering blunt chest trauma but may be falsely elevated in the presence of massive skeletal muscle injury. Cardiac troponin levels are more specific for identifying cardiac injury in this setting. Echocardiography is useful in detecting structural and functional sequelae of contusion, including wall motion abnormalities, pericardial effusion, valvular dysfunction, and ventricular rupture. Although radionuclide scanning can detect myocardial contusion, its role is limited, given the ease and availability of echocardiography. Rupture of the cardiac valves or their supporting structures, most commonly of the tricuspid or mitral valve, leads to acute valvular incompetence. This complication is usually heralded by the development of a loud murmur, may be associated with rapidly progressive heart failure, and can be diagnosed by either transthoracic or transesophageal echocardiography. The most serious consequence of nonpenetrating injury is myocardial rupture, which may result in hemopericardium and tamponade (free wall rupture) or intracardiac shunting (ventricular septal rupture). Although generally fatal, up to 40% of patients with cardiac rupture have been reported to survive long enough to reach a specialized trauma center. Hemopericardium may also result from traumatic rupture of a pericardial vessel or a coronary artery.Additionally, a pericardial effusion may develop weeks or even months after blunt chest trauma as a manifestation of the post-cardiac injury syndrome, which resembles the post-pericardiotomy syndrome (Chap. 22). Blunt, nonpenetrating, often innocent-appearing injuries to the chest may trigger ventricular fibrillation

Occasionally, patients who survive penetrating cardiac 269 injuries may subsequently present with a new cardiac murmur or CHF as a result of mitral regurgitation or an intracardiac shunt (i.e., ventricular or atrial septal defect, aortopulmonary fistula, or coronary AV fistula) that was undetected at the time of their initial injury or developed subsequently. Therefore, trauma patients should be carefully examined several weeks after their injury. If a mechanical complication is suspected, it can be confirmed by echocardiography or cardiac catheterization.

Treatment: TRAUMATIC CARDIAC INJURY

The treatment of an uncomplicated myocardial contusion is similar to that for a myocardial infarction, except that anticoagulation is contraindicated, and should include monitoring for the development of arrhythmias and mechanical complications such as cardiac rupture (Chap. 35). Acute myocardial failure resulting from traumatic valve rupture usually requires urgent operative correction. Immediate thoracotomy should be carried out for most cases of penetrating injury or if there is evidence of cardiac tamponade and/or shock regardless of the type of trauma. Pericardiocentesis may be lifesaving in patients with tamponade but is usually only a temporizing maneuver while they await definitive surgical therapy. Pericardial hemorrhage often leads to constriction (Chap. 22), which must be treated by decortication.

BURKE A et al: Cardiac tumors: an update. Heart 94:117, 2008 KALRA MK, ABBARA S: Imaging cardiac tumors. Cancer Treat Res 143:177, 2008 MATTOX KL: Traumatic heart disease, in Braunwald’s Heart Disease, 7th ed, DP Zipes et al (eds). Philadelphia, Saunders, 2005 PRETRE R, CHILCOTT M: Blunt trauma to the heart and great vessels. N Engl J Med 336:626, 1997 REYMAN K: Cardiac myxomas. N Engl J Med 333:1610, 1995 RHEE PM et al: Penetrating cardiac injuries: A population-based study. J Trauma 45:366, 1998 SABATINE M, SCHOEN F: Primary tumors of the heart, in Braunwald’s Heart Disease, 7th ed, DP Zipes et al (eds). Philadelphia, Saunders, 2005 SIMMERS TA et al: Traumatic papillary muscle rupture. Ann Thorac Surg 72:257, 2001 SYBRANDY KC et al: Diagnosing cardiac contusion: Old wisdom and new insights. Heart 89:485, 2003 TYBURSKI JG et al: Factors affecting prognosis with penetrating wounds of the heart. J Trauma 48:587, 2000 VAUGHAN CJ et al:Tumors and the heart: Molecular genetic advances. Curr Opin Cardiol 16:195, 2001

Tumors and Trauma of the Heart

FURTHER READINGS

CHAPTER 23

even in absence of overt signs of injury. This syndrome, referred to as commotio cordis, occurs most often in adolescents during sporting events (e.g., baseball, hockey, football, and lacrosse) and likely results from an impact to the chest wall overlying the heart during the susceptible phase of repolarization just prior to the peak of the T wave. Survival depends on prompt defibrillation. Sudden emotional or physiologic trauma may precipitate a transient cardiomyopathy that is characterized by dysfunction of the mid-portion and apex of the left ventricle with hyperdynamic function at the ventricular base. This syndrome, referred to as Tako-Tsubo syndrome or the apical ballooning syndrome, is more common in women and usually presents with chest pain, anterior ST-segment elevation, and mildly elevated cardiac enzymes despite the absence of significant epicardial coronary artery disease. The pathophysiology of this syndrome likely relates to catecholamine excess, and possibly to coronary vasospasm.The prognosis is favorable, and complete and spontaneous resolution of the ventricular dysfunction usually occurs within several weeks. Rupture of the aorta, usually just above the aortic valve or at the site of the ligamentum arteriosum, is a common consequence of nonpenetrating chest trauma and is the most common vascular deceleration injury. The clinical presentation is similar to that of aortic dissection (Chap. 38).The arterial pressure and pulse amplitude may be increased in the upper extremities and decreased in the lower extremities, and chest x-ray may reveal mediastinal widening. Occasionally, aortic rupture is contained by the aortic adventitia, resulting in a false, or pseudo-, aneurysm that may be discovered months or years after the initial injury. Penetrating injuries of the heart produced by knife or bullet wounds usually result in rapid clinical deterioration and frequently in death as a result of hemopericardium/ pericardial tamponade or massive hemorrhage. Nonetheless, up to 50% of such patients may survive long enough to reach a specialized trauma center if immediate resuscitation is performed. Prognosis in these patients relates to the mechanism of injury, their clinical condition at presentation, and the specific cardiac chamber(s) involved. Iatrogenic cardiac or coronary arterial perforation may occur as a complication during placement of central venous or intracardiac catheters, pacemaker leads, or intracoronary stents and is associated with a better prognosis than other forms of penetrating cardiac trauma. Traumatic rupture of a great vessel from penetrating injury is usually associated with hemothorax and, less often, hemopericardium. Local hematoma formation may compress major vessels and produce ischemic symptoms, and AV fistulae may develop, occasionally resulting in high-output CHF.

CHAPTER 24

CARDIAC MANIFESTATIONS OF SYSTEMIC DISEASE Eric H. Awtry

■

Wilson S. Colucci

Diabetes Mellitus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 270 Malnutrition and Vitamin Deficiency . . . . . . . . . . . . . . . . . . . 271 Obesity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Thyroid Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Malignant Carcinoid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Pheochromocytoma . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Acromegaly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Rheumatoid Arthritis and the Collagen Vascular Diseases . . . 273 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 274

is more common in diabetics, accounting for up to 90% of their ischemic episodes.Thus, one must have a low threshold for suspecting CAD in diabetic patients.The treatment of diabetics with CAD must include aggressive risk factor management. Pharmacologic therapy and revascularization are similar in diabetics and nondiabetics, excepting that diabetics have greater morbidity and mortality associated with revascularization, have an increased risk of restenosis after percutaneous coronary intervention (PCI), and likely have improved survival when treated with surgical bypass compared with PCI for multivessel CAD. Patients with diabetes mellitus may also have abnormal left ventricular systolic and diastolic function, reflecting concomitant epicardial CAD and hypertension, coronary microvascular disease, endothelial dysfunction, ventricular hypertrophy, and autonomic dysfunction. A restrictive cardiomyopathy may be present with abnormal myocardial relaxation and elevated ventricular filling pressures. Histologically, interstitial fibrosis is seen, and intramural arteries may demonstrate intimal thickening, hyaline deposition, and inflammatory changes. Diabetic patients have an increased risk of developing clinical heart failure, which likely contributes to their excessive cardiovascular morbidity and mortality.There is some evidence that insulin therapy may ameliorate diabetes-related myocardial dysfunction.

The common systemic disorders that have associated cardiac manifestations are summarized in Table 24-1.

DIABETES MELLITUS Diabetes mellitus, both insulin- and non-insulindependent, is an independent risk factor for coronary artery disease [(CAD); Chap. 30], accounting for 14–50% of new cases of cardiovascular disease. Furthermore, CAD is the most common cause of death in adults with diabetes mellitus. In the diabetic population the incidence of CAD relates to the duration of diabetes and the level of glycemic control, and its pathogenesis involves endothelial dysfunction, increased lipoprotein peroxidation, increased inflammation, a prothrombotic state, and associated metabolic abnormalities. Diabetic patients are more likely to suffer a myocardial infarction (MI), have a greater burden of CAD, have larger infarct size, and suffer more postinfarct complications, including heart failure, shock, and death, than nondiabetics. Importantly, diabetic patients are more likely to have atypical ischemic symptoms; nausea, dyspnea, pulmonary edema, arrhythmias, heart block, or syncope may be their anginal equivalent. Additionally,“silent ischemia,” resulting from autonomic nervous system dysfunction,

270

TABLE 24-1 COMMON SYSTEMIC DISORDERS AND THEIR ASSOCIATED CARDIAC MANIFESTATIONS SYSTEMIC DISORDER

COMMON CARDIAC MANIFESTATIONS

Diabetes mellitus

CAD, atypical angina, CMP, systolic or diastolic CHF Dilated CMP, CHF

Protein-calorie malnutrition Thiamine deficiency Hyperhomocysteinemia Obesity Hyperthyroidism Hypothyroidism

Malignant carcinoid Pheochromocytoma Acromegaly Rheumatoid arthritis

Seronegative arthropathies

HIV

Sarcoidosis

Hemochromatosis Marfan syndrome

Ehlers-Danlos syndrome

Note: CAD, coronary artery disease; CHF, congestive heart failure; CMP, cardiomyopathy; SVT, supraventricular tachycardia.

MALNUTRITION AND VITAMIN DEFICIENCY Malnutrition In patients whose intake of protein, calories, or both is severely deficient, the heart may become thin, pale, and hypokinetic with myofibrillar atrophy and interstitial edema. The systolic pressure and cardiac output fall, and the pulse pressure narrows. Generalized edema is

Generalized malnutrition is often accompanied by thiamine deficiency, although this hypovitaminosis may also occur in the presence of an adequate protein and caloric intake, particularly in the Far East where polished rice deficient in thiamine may be a major dietary component. In Western nations where the use of thiamineenriched flour is widespread, clinical thiamine deficiency is limited primarily to alcoholics, food faddists, and patients receiving chemotherapy. Nonetheless, when thiamine stores are measured using the thiamine-pyrophosphate effect (TPPE), thiamine deficiency has been found in 20–90% of patients with chronic heart failure.This deficiency appears to result from both reduced dietary intake and a diuretic-induced increase in the urinary excretion of thiamine. The acute administration of thiamine to these patients increases the left ventricular ejection fraction and the excretion of salt and water. Clinically, patients with thiamine deficiency usually have evidence of generalized malnutrition, peripheral neuropathy, glossitis, and anemia.The classic cardiovascular syndrome is characterized by high-output heart failure, tachycardia, and often elevated left and right ventricular filling pressures.The major cause of the high-output state is vasomotor depression leading to reduced systemic vascular resistance, the precise mechanism of which is not understood.The cardiac examination reveals a wide pulse pressure, tachycardia, a third heart sound, and, frequently, an apical systolic murmur.The ECG may reveal decreased voltage, a prolonged QT interval, and T-wave abnormalities. The chest x-ray generally reveals cardiomegaly and signs of congestive heart failure (CHF).The response to thiamine is often dramatic, with an increase in systemic vascular resistance, a decrease in cardiac output, clearing of pulmonary congestion, and a reduction in heart size often occurring in 12–48 h. Although the response to inotropes and diuretics may be poor before thiamine therapy, these agents may be important after thiamine is given, since the left ventricle may not be able to handle the increased work load presented by the return of vascular tone.

Cardiac Manifestations of Systemic Disease

Amyloidosis

Thiamine Deficiency (Beriberi)

CHAPTER 24

Systemic lupus erythematosus

High-output failure, dilated CMP Premature atherosclerosis CMP, systolic or diastolic CHF Palpitations, SVT, atrial fibrillation, hypertension Hypotension, bradycardia, dilated CMP, CHF, pericardial effusion Tricuspid and pulmonary valve disease, right heart failure Hypertension, palpitations, CHF Systolic or diastolic heart failure Pericarditis, pericardial effusions, coronary arteritis, myocarditis, valvulitis Aortitis, aortic and mitral insufficiency, conduction abnormalities Pericarditis, Libman-Sacks endocarditis, myocarditis, arterial and venous thrombosis Myocarditis, dilated CMP, pericardial effusion CHF, restrictive CMP, valvular regurgitation, pericardial effusion CHF, dilated or restrictive CMP, ventricular arrhythmias, heart block CHF, arrhythmias, heart block Aortic aneurysm and dissection, aortic insufficiency, mitral valve prolapse Aortic and coronary aneurysms, mitral and tricuspid valve prolapse

common and relates to a variety of factors, including 271 reduced serum oncotic pressure and myocardial dysfunction. Such profound states of protein and calorie malnutrition, termed kwashiorkor and marasmus, respectively, are most common in underdeveloped countries. However, significant nutritional heart disease may also occur in developed nations, particularly in patients with chronic diseases such as AIDS, in patients with anorexia nervosa, and in patients with severe cardiac failure in whom gastrointestinal hypoperfusion and venous congestion may lead to anorexia and malabsorption. Open-heart surgery poses increased risk in malnourished patients, and they may benefit from preoperative hyperalimentation.

272 Vitamin B6 , B12 , and Folate Deficiency Vitamins B6, B12, and folate are cofactors in the metabolism of homocysteine. Their deficiency probably contributes to the majority of cases of hyperhomocysteinemia, a disorder associated with increased atherosclerotic risk. Supplementation of these vitamins has reduced the incidence of hyperhomocysteinemia in the United States; however, the clinical cardiovascular benefit of normalizing elevated homocysteine levels remains unproven.

OBESITY

SECTION IV Disorders of the Heart

Severe obesity, especially abdominal obesity, is associated with an increase in cardiovascular morbidity and mortality. Although obesity itself is not considered a disease, it is associated with an increased prevalence of hypertension, glucose intolerance, and atherosclerotic CAD. In addition, obese patients have a distinct cardiovascular abnormality characterized by increased total and central blood volumes, cardiac output, and left ventricular filling pressure. The elevated cardiac output appears to be required to support the metabolic needs of the excess adipose tissue. Left ventricular filling pressure is often at the upper limits of normal at rest and rises excessively with exercise. As a result of chronic volume overload, eccentric cardiac hypertrophy with cardiac dilatation and ventricular dysfunction may develop. Pathologically, there are left and, in some cases, right ventricular hypertrophy and generalized cardiac dilatation. Pulmonary congestion, peripheral edema, and exercise intolerance may all ensue; however, the recognition of these findings may be difficult in massively obese patients. Weight reduction is the most effective therapy and results in reduction in blood volume and in the return of cardiac output toward normal. However, rapid weight reduction may be dangerous, as cardiac arrhythmias and sudden death owing to electrolyte imbalance have been described. Treatment with angiotensin-converting enzyme inhibitors, sodium restriction, and diuretics may be useful to control heart failure symptoms. This form of heart disease should be distinguished from the Pickwickian syndrome, which may share several of the cardiovascular features of heart disease secondary to severe obesity but, in addition, frequently has components of central apnea, hypoxemia, pulmonary hypertension, and cor pulmonale.

THYROID DISEASE Thyroid hormone exerts a major influence on the cardiovascular system by a number of direct and indirect mechanisms and, not surprisingly, cardiovascular effects are prominent in both hypo- and hyperthyroidism. Thyroid hormone causes increases in total-body metabolism and oxygen consumption that indirectly increase

the cardiac workload. In addition, thyroid hormone exerts direct inotropic, chronotropic, and dromotropic effects that are similar to those seen with adrenergic stimulation (e.g., tachycardia, increased cardiac output); they are mediated at least partly by both transcriptional and nontranscriptional effects of thyroid hormone on myosin, calcium-activated ATPase, Na+,K+-ATPase, and myocardial β-adrenergic receptors. Hyperthyroidism Common cardiovascular manifestations of hyperthyroidism include palpitations, systolic hypertension, and fatigue. Sinus tachycardia is present in ∼40% of patients and atrial fibrillation in ∼15%. Physical examination may reveal a hyperdynamic precordium, a widened pulse pressure, increases in the intensity of the first heart sound and the pulmonic component of the second heart sound, and a third heart sound. An increased incidence of mitral valve prolapse has been described in hyperthyroid patients, in which case a midsystolic murmur may be heard at the left sternal border with or without a systolic ejection click. A systolic pleuropericardial friction rub (Means-Lerman scratch) may be heard at the left second intercostal space during expiration and is thought to result from the hyperdynamic cardiac motion. Elderly patients with hyperthyroidism may present with only cardiovascular manifestations of thyrotoxicosis, such as sinus tachycardia, atrial fibrillation, and hypertension, all of which may be resistant to therapy until the hyperthyroidism is controlled. Angina pectoris and CHF are unusual with hyperthyroidism unless there is coexistent heart disease; in such cases, symptoms often resolve with treatment of the hyperthyroidism. Hypothyroidism Cardiac manifestations of hypothyroidism include a reduction in cardiac output, stroke volume, heart rate, blood pressure, and pulse pressure. Pericardial effusions are present in about one-third of patients, rarely progress to tamponade, and likely result from increased capillary permeability. Other clinical signs include cardiomegaly, bradycardia, weak arterial pulses, distant heart sounds, and pleural effusions. Although the signs and symptoms of myxedema may mimic those of CHF, in the absence of other cardiac disease, myocardial failure is uncommon. The ECG generally reveals sinus bradycardia and low voltage, and may show prolongation of the QT interval, decreased P-wave voltage, prolonged AV conduction time, intraventricular conduction disturbances, and nonspecific ST-T wave abnormalities. Chest x-ray may show cardiomegaly, often with a “water bottle” configuration, pleural effusions, and, in some cases, evidence of CHF. Pathologically, the heart is pale and dilated, and often demonstrates myofibrillar swelling, loss of striations, and interstitial fibrosis.

Patients with hypothyroidism frequently have elevations of cholesterol and triglycerides, resulting in premature atherosclerotic CAD. Before treatment with thyroid hormone, patients with hypothyroidism frequently do not have angina pectoris, presumably because of the low metabolic demands caused by their condition. However, angina and MI may be precipitated during initiation of thyroid hormone replacement, especially in elderly patients with underlying heart disease. Therefore, replacement should be done with care, starting with low doses that are increased gradually.

MALIGNANT CARCINOID

ACROMEGALY Exposure of the heart to excessive growth hormone may cause CHF as a result of high cardiac output, diastolic dysfunction owing to ventricular hypertrophy (with increased left ventricular chamber size or wall thickness), or global systolic dysfunction. Hypertension occurs in up to onethird of patients with acromegaly and is characterized by suppression of the renin-angiotensin-aldosterone axis and increases in total-body sodium and plasma volume. Some form of cardiac disease occurs in about one-third of patients with acromegaly and is associated with a doubling of the risk of cardiac death.

RHEUMATOID ARTHRITIS AND THE COLLAGEN VASCULAR DISEASES Rheumatoid Arthritis

PHEOCHROMOCYTOMA

Seronegative Arthropathies

In addition to causing labile or sustained hypertension, the high circulating levels of catecholamines resulting from a pheochromocytoma may also cause direct myocardial injury. Focal myocardial necrosis and inflammatory cell infiltration are present in ∼50% of patients who die with pheochromocytoma and may contribute to clinically significant left ventricular failure and pulmonary edema. In addition, associated hypertension results in left

The seronegative arthropathies, including ankylosing spondylitis, reactive arthritis, psoriatic arthritis, and the arthritides associated with ulcerative colitis and regional enteritis, are all strongly associated with the HLA-B27 histocompatibility antigen and may be accompanied by a pancarditis and proximal aortitis.The aortic inflammation is usually limited to the aortic root but may extend to involve the aortic valve, mitral valve, and ventricular

Cardiac Manifestations of Systemic Disease

Rheumatoid arthritis may be associated with inflammatory changes in any or all cardiac structures, although pericarditis is the most common clinical entity. Pericardial effusions may be found echocardiographically in 10–50% of patients with rheumatoid arthritis, particularly those with subcutaneous nodules. Nonetheless, only a small percentage of these patients have symptomatic pericarditis and, when present, it usually follows a benign course, only occasionally progressing to cardiac tamponade or constrictive pericarditis. The pericardial fluid is generally exudative, with decreased concentrations of complement and glucose and elevated cholesterol. Coronary arteritis with intimal inflammation and edema is present in ∼20% of cases but only rarely results in angina pectoris or MI. Inflammation and granuloma formation may affect the cardiac valves, most often the mitral and aortic, and may cause clinically significant regurgitation owing to valve deformity. Myocarditis is uncommon and rarely results in cardiac dysfunction. Treatment is directed at the underlying rheumatoid arthritis and may include glucocorticoids. Urgent pericardiocentesis should be performed in patients with tamponade, whereas pericardiectomy is usually required in cases of pericardial constriction.

CHAPTER 24

Carcinoid tumors most often originate in the small bowel and elaborate a variety of vasoactive amines (e.g., serotonin), kinins, indoles, and prostaglandins that are believed to be responsible for the diarrhea, flushing, and labile blood pressure that characterize the carcinoid syndrome. Some 50% of patients with carcinoid syndrome have cardiac involvement, usually manifesting as abnormalities of the right-sided cardiac structures.These patients invariably have hepatic metastases allowing vasoactive substances to circumvent hepatic metabolism. Left-sided cardiac involvement is rare and indicates either pulmonary carcinoid or an intracardiac shunt. Pathologically, carcinoid lesions are fibrous plaques that consist of smooth-muscle cells embedded in a stroma of glycosaminoglycans and collagen. They occur on the cardiac valves where they cause valvular dysfunction, as well as on the endothelium of the cardiac chambers and great vessels. Carcinoid heart disease most often presents as tricuspid regurgitation, pulmonic stenosis, or both. In some cases a high cardiac output state may occur, presumably as a result of a decrease in systemic vascular resistance resulting from vasoactive substances released by the tumor. Treatment with somatostatin analogues (e.g., octreotide) or interferon-α improves symptoms and survival in patients with carcinoid heart disease but does not appear to improve valvular abnormalities. In some severely symptomatic patients, valve replacement is indicated. Coronary artery spasm, presumably due to a circulating vasoactive substance, may occur in patients with carcinoid syndrome.

ventricular hypertrophy. Left ventricular dysfunction and 273 CHF may resolve after removal of the tumor.

274 myocardium, resulting in aortic and mitral regurgitation, conduction abnormalities, and ventricular dysfunction. One-tenth of patients have significant aortic insufficiency and one-third have conduction disturbances; both are more common in patients with peripheral joint involvement and long-standing disease. Treatment with aortic valve replacement and permanent pacemaker placement may be required. Occasionally, aortic regurgitation precedes the onset of arthritis, and, therefore, the diagnosis of a seronegative arthritis should be considered in young males with isolated aortic regurgitation. Systemic Lupus Erythematosus (SLE)

SECTION IV

A significant percentage of patients with SLE have cardiac involvement. Pericarditis is common, occurring in about two-thirds of patients, and generally follows a benign course, although rarely tamponade or constriction may result. The characteristic endocardial lesions of SLE are verrucous valvular abnormalities, known as Libman Sacks endocarditis.They are most often located on the left-sided cardiac valves, particularly on the ventricular surface of the posterior mitral leaflet, and are made up almost entirely of fibrin. The lesions may embolize or become infected but rarely cause hemodynamically important valvular regurgitation. Myocarditis generally

parallels the activity of the disease and, although common histologically, seldom results in clinical heart failure unless associated with hypertension. While arteritis of epicardial coronary arteries may occur, it rarely results in myocardial ischemia.There is, however, an increased incidence of coronary atherosclerosis that likely is related more to associated risk factors and glucocorticoid use than to SLE itself. Patients with the antiphospholipid antibody syndrome may have a higher incidence of cardiovascular abnormalities, including valvular regurgitation, venous and arterial thrombosis, premature stroke, MI, pulmonary hypertension, and cardiomyopathy. FURTHER READINGS BRUCE IN:“Not only . . . but also”: Factors that contribute to accelerated atherosclerosis and premature coronary artery disease in systemic lupus erythematosus. Rheumatology 44:1492, 2005 FOX DJ, KHATTAR RS: Carcinoid heart disease: Presentation, diagnosis, and management. Heart 90:1224, 2004 GRUNDY SM et al: Prevention Conference VI: Diabetes and cardiovascular disease, executive summary. Circulation 105:2231, 2002 HOFFMAN GS: Rheumatic diseases and the heart, in Braunwald’s Heart Disease, 7th ed, DP Zipes et al (eds). Philadelphia, Saunders, 2005 KENCHAIAH S et al: Obesity and the risk of heart failure. N Engl J Med 347:305, 2002 KLEIN I, OJAMAA K:Thyroid hormone and the cardiovascular system. N Engl J Med 344:501, 2001

Disorders of the Heart

CHAPTER 25

INFECTIVE ENDOCARDITIS Adolf W. Karchmer

Etiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Pathogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Clinical Manifestations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 Prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 288 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289

shifted from chronic rheumatic heart disease to illicit IV drug use, degenerative valve disease, intracardiac devices, and health care–associated infection. The incidence of endocarditis is notably increased among the elderly. In reported series, 10–30% of endocarditis cases involve prosthetic valves. The risk of prosthesis infection is greatest during the first 6 months after valve replacement; gradually declines to a low, stable rate thereafter; and is similar for mechanical and bioprosthetic devices.

The prototypic lesion of infective endocarditis, the vegetation (Fig. 25-1), is a mass of platelets, fibrin, microcolonies of microorganisms, and scant inflammatory cells. Infection most commonly involves heart valves (either native or prosthetic) but may also occur on the low-pressure side of the ventricular septum at the site of a defect, on the mural endocardium where it is damaged by aberrant jets of blood or foreign bodies, or on intracardiac devices themselves. The analogous process involving arteriovenous shunts, arterioarterial shunts (patent ductus arteriosus), or a coarctation of the aorta is called infective endarteritis. Endocarditis may be classified according to the temporal evolution of disease, the site of infection, the cause of infection, or a predisposing risk factor such as injection drug use. Although each classification criterion provides therapeutic and prognostic insight, none is sufficient alone. Acute endocarditis is a hectically febrile illness that rapidly damages cardiac structures, hematogenously seeds extracardiac sites, and, if untreated, progresses to death within weeks. Subacute endocarditis follows an indolent course; causes structural cardiac damage only slowly, if at all; rarely metastasizes; and is gradually progressive unless complicated by a major embolic event or ruptured mycotic aneurysm. In developed countries, the incidence of endocarditis ranges from 2.6–7.0 cases per 100,000 population per year and remained relatively stable from 1950–2000. While rates of congenital heart diseases remain constant, other predisposing conditions in developed countries have

ETIOLOGY Although many species of bacteria and fungi cause sporadic episodes of endocarditis, only a few bacterial species cause the majority of cases (Table 25-1).The pathogens vary somewhat with the clinical types of endocarditis, in part because of different portals of entry.The oral cavity, skin, and upper respiratory tract are the respective primary portals for the viridans streptococci, staphylococci, and HACEK organisms (Haemophilus, Actinobacillus, Cardiobacterium, Eikenella, and Kingella) causing community-acquired native valve endocarditis. Streptococcus bovis originates from the gastrointestinal tract, where it is associated with polyps and colonic tumors, and enterococci enter the bloodstream from the genitourinary tract. Health care–associated native valve endocarditis is the consequence of bacteremia arising from intravascular catheter infections, nosocomial wound and urinary tract infections, and chronic invasive procedures such as hemodialysis. Endocarditis complicates

275

Prosthetic valve endocarditis arising within 2 months of valve surgery is generally the result of intraoperative contamination of the prosthesis or a bacteremic postoperative complication. The nosocomial nature of these infections is reflected in their primary microbial causes: coagulase-negative staphylococci (CoNS), S. aureus, facultative gram-negative bacilli, diphtheroids, and fungi. The portals of entry and organisms causing cases beginning >12 months after surgery are similar to those in community-acquired native valve endocarditis. Epidemiologic evidence suggests that prosthetic valve endocarditis due to CoNS that presents 2–12 months after surgery often represents delayed-onset nosocomial infection. At least 85% of CoNS strains that cause prosthetic valve endocarditis within 12 months of surgery are methicillinresistant; the rate of methicillin resistance decreases to 25% among CoNS strains causing prosthetic valve endocarditis that presents >1 year after valve surgery. Transvenous pacemaker lead– and/or implanted defibrillator–associated endocarditis is usually nosocomial. The majority of episodes occur within weeks of implantation or generator change and are caused by S. aureus or CoNS.

276

FIGURE 25-1 Vegetations (arrows) due to viridans streptococcal endocarditis involving the mitral valve.

6–25% of episodes of catheter-associated Staphylococcus aureus bacteremia; the higher rates are detected by careful transesophageal echocardiography (TEE) screening (see Echocardiography later in the chapter).

SECTION IV

TABLE 25-1 ORGANISMS CAUSING MAJOR CLINICAL FORMS OF ENDOCARDITIS PERCENT OF CASES

Disorders of the Heart

ORGANISM

Streptococcib Pneumococci Enterococci Staphylococcus aureus Coagulase-negative staphylococci Fastidious gramnegative coccobacilli (HACEK group)d Gram-negative bacilli Candida spp. Polymicrobial/ miscellaneous Diphtheroids Culture-negative a

NATIVE VALVE ENDOCARDITIS

PROSTHETIC VALVE ENDOCARDITIS AT INDICATED TIME OF ONSET (MONTHS) AFTER VALVE SURGERY

COMMUNITYACQUIRED (n = 683)

12 (n = 194)

ENDOCARDITIS IN INJECTION DRUG USERS RIGHTSIDED (n = 346)

LEFTSIDED (n = 204)

TOTAL (n = 675)a

32 1 8 35 4

8 — 16 44c 15

1 — 8 22 33

9 — 12 12 32

31 — 11 18 11

5 — 2 77 —

15 — 24 23 —

12 — 9 57 —

3

—

—

—

6

—

—

—

3 1

5 6

13 8

3 12

6 1

5 —

13 12

7 4

6 — 5

1 — 5

3 6 5

6 — 6

5 3 8

8 — 3

10 — 3

7 0.1 3

The total number of cases is larger than the sum of right- and left-sided cases because the location of infection was not specified in some cases. b Includes viridans streptococci; Streptococcus bovis; other non–group A, groupable streptococci; and Abiotrophia spp. (nutritionally variant, pyridoxal-requiring streptococci). c Methicillin resistance is common among these S. aureus strains. d Includes Haemophilus spp., Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella spp., and Kingella spp. Source: Data are compiled from multiple studies.

PATHOGENESIS

Infective Endocarditis

Unless it is injured, the endothelium is resistant to infection by most bacteria and to thrombus formation. Endothelial injury (e.g., at the site of impact of high-velocity blood jets or on the low-pressure side of a cardiac structural lesion) causes aberrant flow and allows either direct infection by virulent organisms or the development of an uninfected platelet-fibrin thrombus—a condition called nonbacterial thrombotic endocarditis (NBTE). The thrombus subsequently serves as a site of bacterial attachment during transient bacteremia.The cardiac conditions most commonly resulting in NBTE are mitral regurgitation, aortic stenosis, aortic regurgitation, ventricular septal defects, and complex congenital heart disease. These conditions result from rheumatic heart disease (particularly in the developing world, where rheumatic fever remains prevalent), mitral valve prolapse, degenerative heart disease, and congenital malformations. NBTE also arises as a result of a hypercoagulable state; this phenomenon gives rise to the clinical entity of marantic endocarditis (uninfected vegetations seen in patients with malignancy and chronic diseases) and to bland vegetations complicating systemic lupus erythematosus and the antiphospholipid antibody syndrome. Organisms that cause endocarditis generally enter the bloodstream from mucosal surfaces, the skin, or sites of focal infection. Except for more virulent bacteria (e.g., S. aureus) that can adhere directly to intact endothelium

or exposed subendothelial tissue, microorganisms in the 277 blood adhere to sites at NBTE. If resistant to the bactericidal activity of serum and the microbicidal peptides released locally by platelets, the organisms proliferate and induce a procoagulant state at the site by eliciting tissue factor from adherent monocytes or, in the case of S. aureus, from monocytes and from intact endothelium. Fibrin deposition combines with platelet aggregation, stimulated by tissue factor and independently by proliferating microorganisms, to generate an infected vegetation. The organisms that commonly cause endocarditis have surface adhesin molecules, collectively called microbial surface components recognizing adhesin matrix molecules (MSCRAMMs) that mediate adherence to NBTE sites or injured endothelium. Fibronectin-binding proteins present on many gram-positive bacteria, clumping factor (a fibrinogen- and fibrin-binding surface protein) on S. aureus, and glucans or FimA (a member of the family of oral mucosal adhesins) on streptococci facilitate adherence. Fibronectin-binding proteins are required for S. aureus invasion of intact endothelium; thus these surface proteins may facilitate infection of previously normal valves. In the absence of host defenses, organisms enmeshed in the growing platelet-fibrin vegetation proliferate to form dense microcolonies. Organisms deep in vegetations are metabolically inactive (nongrowing) and relatively resistant to killing by antimicrobial agents. Proliferating surface organisms are shed into the bloodstream continuously. The pathophysiologic consequences and clinical manifestations of endocarditis—other than constitutional symptoms, which probably result from cytokine production—arise from damage to intracardiac structures; embolization of vegetation fragments, leading to infection or infarction of remote tissues; hematogenous infection of sites during bacteremia; and tissue injury due to the deposition of circulating immune complexes or immune responses to deposited bacterial antigens.

CHAPTER 25

Endocarditis occurring among injection drug users, especially when infection involves the tricuspid valve, is commonly caused by S. aureus strains, many of which are methicillin-resistant. Left-sided valve infections in addicts have a more varied etiology and involve abnormal valves, often ones damaged by prior episodes of endocarditis.A number of these cases are caused by Pseudomonas aeruginosa and Candida species, and sporadic cases are due to unusual organisms such as Bacillus, Lactobacillus, and Corynebacterium species. Polymicrobial endocarditis is more common among injection drug users than among patients who do not inject drugs. The presence of HIV in the former population does not significantly influence the causes of endocarditis. From 5–15% of patients with endocarditis have negative blood cultures; in one-third to one-half of these cases, cultures are negative because of prior antibiotic exposure. The remainder of these patients are infected by fastidious organisms, such as nutritionally variant organisms (now designated Granulicatella and Abiotrophia species), HACEK organisms, and Bartonella species. Some fastidious organisms that cause endocarditis do so in characteristic epidemiologic settings (e.g., Coxiella burnetii in Europe, Brucella species in the Middle East). Tropheryma whipplei causes an indolent, culture-negative, afebrile form of endocarditis.

CLINICAL MANIFESTATIONS The clinical syndrome of infective endocarditis is highly variable and spans a continuum between acute and subacute presentations. Native valve endocarditis (whether acquired in the community or in association with health care), prosthetic valve endocarditis, and endocarditis due to injection drug use share clinical and laboratory manifestations (Table 25-2). The causative microorganism is primarily responsible for the temporal course of endocarditis. β-Hemolytic streptococci, S. aureus, and pneumococci typically result in an acute course, although S. aureus occasionally causes subacute disease. Endocarditis caused by Staphylococcus lugdunensis (a coagulase-negative species) or by enterococci may present acutely. Subacute endocarditis is typically caused by viridans streptococci, enterococci, CoNS, and the HACEK group. Endocarditis

278

TABLE 25-2 CLINICAL AND LABORATORY FEATURES OF INFECTIVE ENDOCARDITIS FEATURE

SECTION IV

Fever Chills and sweats Anorexia, weight loss, malaise Myalgias, arthralgias Back pain Heart murmur New/worsened regurgitant murmur Arterial emboli Splenomegaly Clubbing Neurologic manifestations Peripheral manifestations (Osler’s nodes, subungual hemorrhages, Janeway lesions, Roth’s spots) Petechiae Laboratory manifestations Anemia Leukocytosis Microscopic hematuria Elevated erythrocyte sedimentation rate Elevated C-reactive protein level Rheumatoid factor Circulating immune complexes Decreased serum complement

FREQUENCY, %

80–90 40–75 25–50 15–30 7–15 80–85 10–40 20–50 15–50 10–20 20–40 2–15

10–40 70–90 20–30 30–50 >90 >90 50 65–100 5–40

Disorders of the Heart

caused by Bartonella species and the agent of Q fever, C. burnetii, is exceptionally indolent. The clinical features of endocarditis are nonspecific. However, these symptoms in a febrile patient with valvular abnormalities or a behavior pattern that predisposes to endocarditis (e.g., injection drug use) suggest the diagnosis, as do bacteremia with organisms that frequently cause endocarditis, otherwise-unexplained arterial emboli, and progressive cardiac valvular incompetence. In patients with subacute presentations, fever is typically low-grade and rarely exceeds 39.4°C (103°F); in contrast, temperatures of 39.4°–40°C (103°–104°F) are often noted in acute endocarditis. Fever may be blunted or absent in patients who are elderly or severely debilitated or who have marked cardiac or renal failure.

but occasionally is due to endocarditis-associated myocarditis or an intracardiac fistula. Heart failure due to aortic valve dysfunction progresses more rapidly than does that due to mitral valve dysfunction. Extension of infection beyond valve leaflets into adjacent annular or myocardial tissue results in perivalvular abscesses, which in turn may cause fistulae (from the root of the aorta into cardiac chambers or between cardiac chambers) with new murmurs. Abscesses may burrow from the aortic valve annulus through the epicardium, causing pericarditis. Extension of infection into paravalvular tissue adjacent to either the right or the noncoronary cusp of the aortic valve may interrupt the conduction system in the upper interventricular septum, leading to varying degrees of heart block. Although perivalvular abscesses arising from the mitral valve may potentially interrupt conduction pathways near the atrioventricular node or in the proximal bundle of His, such interruption occurs infrequently. Emboli to a coronary artery may result in myocardial infarction; nevertheless, embolic transmural infarcts are rare. Noncardiac Manifestations The classic nonsuppurative peripheral manifestations of subacute endocarditis are related to the duration of infection and, with early diagnosis and treatment, have become infrequent. In contrast, septic embolization mimicking some of these lesions (subungual hemorrhage, Osler’s nodes) is common in patients with acute S. aureus endocarditis (Fig. 25-2). Musculoskeletal symptoms, including nonspecific inflammatory arthritis and back pain, usually remit promptly with treatment but must be distinguished from focal metastatic infection. Hematogenously seeded focal infection may involve any organ but most often is

Cardiac Manifestations Although heart murmurs are usually indicative of the predisposing cardiac pathology rather than of endocarditis, valvular damage and ruptured chordae may result in new regurgitant murmurs. In acute endocarditis involving a normal valve, murmurs are heard on presentation in only 30–45% of patients but ultimately are detected in 85%. Congestive heart failure develops in 30–40% of patients; it is usually a consequence of valvular dysfunction

FIGURE 25-2 Septic emboli with hemorrhage and infarction due to acute Staphylococcus aureus endocarditis. (Used with permission of L. Baden.)

In almost 50% of patients who have endocarditis associated with injection drug use, infection is limited to the tricuspid valve.These patients present with fever, faint or no murmur, and (in 75% of cases) prominent pulmonary findings related to septic emboli, including cough, pleuritic chest pain, nodular pulmonary infiltrates, and occasionally pyopneumothorax. Infection involving valves on the left side of the heart presents with the typical clinical features of endocarditis. Health care–associated endocarditis (defined as that which is nosocomial, arises after recent hospitalization, or is a direct consequence of long-term indwelling devices) has typical manifestations if it is not associated with a retained intracardiac device. Endocarditis associated with flow-directed pulmonary artery catheters is often cryptic, with symptoms masked by comorbid critical illness, and is commonly diagnosed at autopsy. Transvenous pacemaker lead– and/or implanted defibrillator–associated endocarditis may be associated with obvious or cryptic generator pocket infection and results in fever, minimal murmur, and pulmonary symptoms due to septic emboli.

DIAGNOSIS The Duke Criteria The diagnosis of infective endocarditis is established with certainty only when vegetations obtained at cardiac surgery, at autopsy, or from an artery (an embolus) are examined histologically and microbiologically. Nevertheless, a highly sensitive and specific diagnostic schema— known as the Duke criteria—has been developed on the basis of clinical, laboratory, and echocardiographic findings (Table 25-3). Documentation of two major criteria, of one major and three minor criteria, or of five minor criteria allows a clinical diagnosis of definite endocarditis. The diagnosis of endocarditis is rejected if an alternative diagnosis is established, if symptoms resolve and do not recur with ≤ 4 days of antibiotic therapy, or if surgery or autopsy after ≤ 4 days of antimicrobial therapy yields no histologic evidence of endocarditis. Illnesses not classified as definite endocarditis or rejected are considered cases of possible infective endocarditis when either one major and one minor criterion or three minor criteria are identified. Requiring the identification of clinical features of endocarditis for classification as possible infective endocarditis increases the specificity of the schema without significantly reducing its sensitivity. The roles of bacteremia and echocardiographic findings in the diagnosis of endocarditis are appropriately emphasized in the Duke criteria. The requirement for multiple positive blood cultures over time is consistent with the continuous low-density bacteremia characteristic of endocarditis (≤100 organisms/mL). Among patients with untreated endocarditis who ultimately have a positive blood culture, 95% of all blood cultures are positive; in 98% of these cases, one of the initial two sets of cultures yields the microorganism. The diagnostic criteria attach significance to the species of organism isolated from blood cultures. To fulfill a major criterion, the isolation of an organism that causes both endocarditis and bacteremia in the absence of endocarditis (e.g., S. aureus, enterococci) must take place repeatedly (i.e., persistent bacteremia) and in the absence of a primary focus of infection. Organisms that rarely cause endocarditis but commonly contaminate blood cultures (e.g., diphtheroids, CoNS) must be isolated repeatedly if their isolation is to serve as a major criterion.

Infective Endocarditis

Manifestations of Specific Predisposing Conditions

Late-onset prosthetic valve endocarditis presents with 279 typical clinical features. Cases arising within 60 days of valve surgery (early onset) lack peripheral vascular manifestations, and typical symptoms may be obscured by comorbidity associated with recent surgery. In both early-onset and more delayed presentations, paravalvular infection is common and often results in partial valve dehiscence, regurgitant murmurs, congestive heart failure, or disruption of the conduction system.

CHAPTER 25

clinically evident in the skin, spleen, kidneys, skeletal system, and meninges. Arterial emboli are clinically apparent in up to 50% of patients.Vegetations >10 mm in diameter (as measured by echocardiography) and those located on the mitral valve are more likely to embolize than are smaller or nonmitral vegetations. Embolic events—often with infarction—involving the extremities, spleen, kidneys, bowel, or brain are often noted at presentation.With effective antibiotic treatment, the frequency of embolic events decreases from 13 per 1000 patient-days during the initial week to 1.2 per 1000 patient-days after the third week. Emboli occurring late during or after effective therapy do not in themselves constitute evidence of failed antimicrobial treatment. Neurologic symptoms, most often resulting from embolic strokes, occur in up to 40% of patients. Other neurologic complications include aseptic or purulent meningitis, intracranial hemorrhage due to hemorrhagic infarcts or ruptured mycotic aneurysms, seizures, and encephalopathy. (Mycotic aneurysms are focal dilations of arteries occurring at points in the artery wall that have been weakened by infection in the vasa vasorum or where septic emboli have lodged.) Microabscesses in brain and meninges occur commonly in S. aureus endocarditis; surgically drainable intracerebral abscesses are infrequent. Immune complex deposition on the glomerular basement membrane causes diffuse hypocomplementemic glomerulonephritis and renal dysfunction, which typically improve with effective antimicrobial therapy. Embolic renal infarcts cause flank pain and hematuria but rarely cause renal dysfunction.

280

TABLE 25-3 THE DUKE CRITERIA FOR THE CLINICAL DIAGNOSIS OF INFECTIVE ENDOCARDITIS Major Criteria

SECTION IV

1. Positive blood culture Typical microorganism for infective endocarditis from two separate blood cultures Viridans streptococci, Streptococcus bovis, HACEK group, Staphylococcus aureus, or Community-acquired enterococci in the absence of a primary focus, or Persistently positive blood culture, defined as recovery of a microorganism consistent with infective endocarditis from: Blood cultures drawn >12 h apart; or All of three or a majority of four or more separate blood cultures, with first and last drawn at least 1 h apart Single positive blood culture for Coxiella burnetii or phase I IgG antibody titer of >1:800 2. Evidence of endocardial involvement Positive echocardiograma Oscillating intracardiac mass on valve or supporting structures or in the path of regurgitant jets or in implanted material, in the absence of an alternative anatomic explanation, or Abscess, or New partial dehiscence of prosthetic valve, or New valvular regurgitation (increase or change in preexisting murmur not sufficient) Minor Criteria

Disorders of the Heart

1. Predisposition: predisposing heart condition or injection drug use 2. Fever ≥38.0°C (≥100.4°F) 3. Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, Janeway lesions 4. Immunologic phenomena: glomerulonephritis, Osler’s nodes, Roth’s spots, rheumatoid factor 5. Microbiologic evidence: positive blood culture but not meeting major criterion as noted previouslyb or serologic evidence of active infection with organism consistent with infective endocarditis a

Transesophageal echocardiography is recommended for assessing possible prosthetic valve endocarditis or complicated endocarditis. b Excluding single positive cultures for coagulase-negative staphylococci and diphtheroids, which are common culture contaminants, and organisms that do not cause endocarditis frequently, such as gram-negative bacilli. Note: HACEK, Haemophilus spp., Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella species. Source: Adapted from Li et al., with permission from the University of Chicago Press.

Blood Cultures Isolation of the causative microorganism from blood cultures is critical not only for diagnosis but also for determination of antimicrobial susceptibility and planning of treatment. In the absence of prior antibiotic therapy, three

blood culture sets (with two bottles per set), separated from each other by at least 1 h, should be obtained from different venipuncture sites over 24 h. If the cultures remain negative after 48–72 h, two or three additional blood culture sets should be obtained, and the laboratory should be consulted for advice regarding optimal culture techniques. Empirical antimicrobial therapy should not be administered initially to hemodynamically stable patients with subacute endocarditis, especially those who have received antibiotics within the preceding 2 weeks; thus, if necessary, additional blood culture sets can be obtained without the confounding effect of empirical treatment. Patients with acute endocarditis or with deteriorating hemodynamics who may require urgent surgery should be treated empirically immediately after three sets of blood cultures are obtained over several hours. Non-Blood-Culture Tests Serologic tests can be used to implicate causally some organisms that are difficult to recover by blood culture: Brucella, Bartonella, Legionella, and C. burnetii. Pathogens can also be identified in surgically recovered vegetations or emboli by culture, by microscopic examination with special stains (i.e., the periodic acid–Schiff stain for T. whipplei), and by use of polymerase chain reaction (PCR) to recover unique microbial DNA or 16S rRNA that, when sequenced, allows identification of organisms. Echocardiography Imaging with echocardiography allows anatomic confirmation of infective endocarditis, sizing of vegetations, detection of intracardiac complications, and assessment of cardiac function (Fig. 25-3). Transthoracic echocardiography (TTE) is noninvasive and exceptionally specific; however, it cannot image vegetations 90% of patients with definite endocarditis; nevertheless, falsenegative studies are noted in 6–18% of endocarditis patients. TEE is the optimal method for the diagnosis of prosthetic endocarditis or the detection of myocardial abscess, valve perforation, or intracardiac fistulae. Experts favor echocardiographic evaluation of all patients with a clinical diagnosis of endocarditis; however, the test should not be used to screen patients with a low probability of endocarditis (e.g., patients with unexplained fever). An American Heart Association approach to the use of echocardiography for evaluation of patients with suspected endocarditis is illustrated in Fig. 25-4. A negative TEE when endocarditis is likely does not exclude the diagnosis but rather warrants repetition of the study in 7–10 days.

281

FIGURE 25-3 Imaging of a mitral valve infected with Staphylococcus aureus by low-esophageal four-chamber-view transesophageal echocardiography (TEE). A. Two-dimensional echocardiogram showing a large vegetation with an adjacent echolucent abscess cavity. B. Color-flow Doppler image showing severe

mitral regurgitation through both the abscess-fistula and the central valve orifice. A, abscess; A-F, abscess-fistula; L, valve leaflets; LA, left atrium; LV, left ventricle; MR, mitral central valve regurgitation; RV, right ventricle; veg, vegetation. (With permission of Andrew Burger, M.D.)

–

Initial TEE

–

+

Low suspicion persists

Increased suspicion during clinical course

TEE

–

Look for other source

+

+

High suspicion persists

Rx

High-risk echo features *

No high-risk echo features

TEE for detection of complications

No TEE unless clinical status deteriorates

Rx

FIGURE 25-4 The diagnostic use of transesophageal and transtracheal echocardiography (TEE and TTE, respectively). †High initial patient risk for endocarditis as listed in Table 25-8 or evidence of intracardiac complications (new regurgitant murmur, new electrocardiographic conduction changes, or congestive heart failure). ∗High-risk echocardiographic features

Look for other source of symptoms

–

Repeat TEE

Rx

+ Alternative diagnosis established

–

+ Rx

Look for other source Follow-up TEE or TTE to reassess vegetations, complications, or Rx response as clinically indicated

include large vegetations, valve insufficiency, paravalvular infection, or ventricular dysfunction. Rx indicates initiation of antibiotic therapy. [Reproduced with permission from Diagnosis and Management of Infective Endocarditis and Its Complications (Circulation 1998; 98:2936-2948. © 1998 American Heart Association.)]

Infective Endocarditis

Initial TTE

CHAPTER 25

High initial patient risk† moderate to high clinical suspicion or difficult imaging candidate

IE suspected

Low initial patient risk and low clinical suspicion

282 Other Studies Many laboratory studies that are not diagnostic—i.e., complete blood count, creatinine determination, liver function tests, chest radiography, and electrocardiography—are nevertheless important in the management of patients with endocarditis. The erythrocyte sedimentation rate, C-reactive protein level, and circulating immune complex titer are commonly increased in endocarditis (Table 25-2). Cardiac catheterization is useful primarily to assess coronary artery patency in older individuals who are to undergo surgery for endocarditis.

Treatment: INFECTIVE ENDOCARDITIS THERAPY It is difficult to eradicate bacteria from the avascular vegetation in infective endocarditis because this site is relatively deficient in host defenses and because the largely nongrowing, metabolically inactive bacteria are less easily killed by antibiotics. To cure endocarditis, all bacteria in the vegetation must be killed; therefore, therapy must be bactericidal and prolonged. Antibiotics are generally given parenterally and must reach high serum concentrations that will, through passive diffusion, lead to effective concentrations in the depths of the vegetation. The choice of effective therapy requires precise knowledge of the susceptibility of the causative microorganisms. The decision to initiate treatment before a cause is defined must balance the need to establish a microbiologic diagnosis against the potential progression of disease or the need for urgent surgery (see Blood Cultures, earlier in the chapter). The individual vulnerabilities of the patient should be weighed in the selection of therapy— e.g., simultaneous infection at other sites (such as meningitis), allergies, end-organ dysfunction, interactions with concomitant medications, and risks of adverse events. Although given for several weeks longer, the regimens recommended for the treatment of endocarditis involving prosthetic valves (except for staphylococcal infections) are similar to those used to treat native valve infection (Table 25-4). Recommended doses and durations of therapy should be adhered to unless alterations are required by adverse events.

ANTIMICROBIAL

SECTION IV Disorders of the Heart

Organism-Specific Therapies Streptococci To select the optimal therapy for

streptococcal endocarditis, the minimum inhibitory concentration (MIC) of penicillin for the causative isolate must be determined (Table 25-4). The 2-week penicillin/ gentamicin or ceftriaxone/gentamicin regimens should not be used to treat complicated native valve infection or prosthetic valve endocarditis. The regimen

recommended for relatively penicillin-resistant streptococci is advocated for treatment of endocarditis caused by organisms of group B, C, or G. Endocarditis caused by nutritionally variant organisms (Granulicatella or Abiotrophia species) and Gemella morbillorum is treated with the regimen for moderately penicillin-resistant streptococci, as is prosthetic valve endocarditis caused by these organisms or by streptococci with a penicillin MIC of >0.1 µg/mL (Table 25-4). Enterococci Enterococci are resistant to oxacillin,

nafcillin, and the cephalosporins and are only inhibited— not killed—by penicillin, ampicillin, teicoplanin (not available in the United States), and vancomycin. To kill enterococci requires the synergistic interaction of a cell wall–active antibiotic (penicillin, ampicillin, vancomycin, or teicoplanin) that is effective at achievable serum concentrations and an aminoglycoside (gentamicin or streptomycin) to which the isolate does not exhibit high-level resistance. An isolate’s resistance to cell wall–active agents or its ability to replicate in the presence of gentamicin at ≥500 µg/mL or streptomycin at 1000–2000 µg/mL—a phenomenon called high-level aminoglycoside resistance— indicates that the ineffective antimicrobial agent cannot participate in the interaction to produce killing. Highlevel resistance to gentamicin predicts that tobramycin, netilmicin, amikacin, and kanamycin also will be ineffective. In fact, even when enterococci are not highly resistant to gentamicin, it is difficult to predict the ability of these other aminoglycosides to participate in synergistic killing; consequently, they should not in general be used to treat enterococcal endocarditis. Enterococci causing endocarditis must be tested for high-level resistance to streptomycin and gentamicin, β-lactamase production, and susceptibility to penicillin and ampicillin (MIC ≤ 16 µg/mL) and to vancomycin (MIC ≤ 8 µg/mL). If the isolate produces β-lactamase, ampicillin/sulbactam or vancomycin can be used as the cell wall–active component; if the penicillin/ampicillin MIC is >16 µg/mL, vancomycin can be considered; and if the vancomycin MIC is >8 µg/mL, penicillin or ampicillin may be considered. In the absence of high-level resistance, gentamicin or streptomycin should be used as the aminoglycoside (Table 25-4). If there is high-level resistance to both these drugs, no aminoglycoside should be given; instead, an 8- to 12-week course of a single cell wall–active agent is suggested—or, for E. faecalis, high doses of ampicillin plus either ceftriaxone or cefotaxime. If this alternative therapy fails or the isolate is resistant to all of the commonly used agents, surgical treatment is advised. The role of newer agents potentially active against multidrug-resistant enterococci [quinupristin/dalfopristin (E. faecium only), linezolid, and daptomycin] in the treatment of endocarditis has not been established. Although the dose of gentamicin

TABLE 25-4

283

ANTIBIOTIC TREATMENT FOR INFECTIVE ENDOCARDITIS CAUSED BY COMMON ORGANISMSa ORGANISM

DRUG (DOSE, DURATION)

COMMENTS

• Penicillin G (2–3 mU IV q4h for 4 weeks) • Ceftriaxone (2 g/d IV as a single dose

— Can use ceftriaxone in patients with nonimmediate penicillin allergy Use vancomycin in patients with severe or immediate β-lactam allergy Avoid 2-week regimen when risk of aminoglycoside toxicity is increased and in prosthetic valve or complicated endocarditis Penicillin alone at this dose for 6 weeks or with gentamicin during initial 2 weeks preferred for prosthetic valve endocarditis caused by streptococci with penicillin MIC ≤ 0.1 µg/mL — Preferred for prosthetic valve endocarditis caused by streptococci with penicillin MICs of >0.1 µg/mL —

Streptococci Penicillin-susceptibleb streptococci, S. bovis

for 4 weeks)

• Vancomycinc (15 mg/kg IV q12h for 4 weeks)

• Penicillin G (2–3 mU IV q4h) or

Relatively penicillin-resistantf streptococci

ceftriaxone (2 g IV qd) for 2 weeks plus gentamicind (3 mg/kg qd IV or IM, as a single dosee or divided into equal doses q8h for 2 weeks) • Penicillin G (4 mU IV q4h) or ceftriaxone(2 g IV qd) for 4 weeks plus gentamicind (3 mg/kg qd IV or IM, as a single dosee or divided into equal doses q8h for 2 weeks)

• Penicillin G (4–5 mU IV q4h) or

Enterococcih • Penicillin G (4–5 mU IV q4h)

plus gentamicind (1 mg/kg IV q8h), both for 4–6 weeks

• Ampicillin (2 g IV q4h) plus gentamicind

Can use streptomycin (7.5 mg/kg q12h) in lieu of gentamicin if there is not high-level resistance to streptomycin —

(1 mg/kg IV q8h), both for 4–6 weeks • Vancomycinc (15 mg/kg IVq12h) plus

gentamicind (1 mg/kg IV q8h), both for 4–6 weeks

Use vancomycin plus gentamicin for penicillinallergic patients, or desensitize to penicillin

Staphylococci Methicillin-susceptible, infecting native valves (no foreign devices)

• Nafcillin or oxacillin (2 g IV q4h for

4–6 weeks) plus (optional) gentamicind (1 mg/kg IM or IV q8h for 3–5 days) • Cefazolin (2 g IV q8h for 4–6 weeks) plus

(optional) gentamicind (1 mg/kg IM or IV q8h for 3–5 days) • Vancomycinc (15 mg/kg IV q12h for 4–6 weeks)

Can use penicillin (4 mU q4h) if isolate is penicillinsusceptible (does not produce β-lactamase) Can use cefazolin regimen for patients with nonimmediate penicillin Use vancomycin for patients with immediate (urticarial) or severe penicillin allergy

(Continued)

Infective Endocarditis

ceftriaxone (2 g IV qd) for 6 weeks plus gentamicind (3 mg/kg qd IV or IM as a single dosee or divided into equal doses q8h for 6 weeks) • Vancomycinc as noted above for 4 weeks

CHAPTER 25

Vancomycinc as noted above for 4 weeks Moderately penicillin-resistantg streptococci, nutritionally variant organisms, or Gemella morbillorum

284

TABLE 25-4 (CONTINUED) ANTIBIOTIC TREATMENT FOR INFECTIVE ENDOCARDITIS CAUSED BY COMMON ORGANISMSa ORGANISM

DRUG (DOSE, DURATION)

COMMENTS

Methicillin-resistant, infecting native valves (no foreign devices) Methicillin-susceptible, infecting prosthetic valves

• Vancomycinc (15 mg/kg IV q12h

Methicillin-resistant, infecting prosthetic valves

• Vancomycinc (15 mg/kg IV q12h for

No role for routine use of rifampin Use gentamicin during initial 2 weeks; determine susceptibility to gentamicin before initiating rifampin (see text); if patient is highly allergic to penicillin, use regimen for methicillin-resistant staphylococci; if β-lactam allergy is of the minor, nonimmediate type, can substitute cefazolin for oxacillin/nafcillin Use gentamicin during initial 2 weeks; determine gentamicin susceptibility before initiating rifampin (see text)

Streptococci for 4–6 weeks) • Nafcillin or oxacillin (2 g IV q4h for 6–8 weeks) plus gentamicind (1 mg/kg IM or IV q8h for 2 weeks) plus rifampini (300 mg PO q8h for 6–8 weeks)

SECTION IV

6–8 weeks) plus gentamicind (1 mg/kg IM or IV q8h for 2 weeks) plus rifampini (300 mg PO q8h for 6–8 weeks)

HACEK Organisms • Ceftriaxone (2 g/d IV as a single dose for

4 weeks)

Disorders of the Heart

• Ampicillin/sulbactam (3 g IV q6h for 4 weeks)

Can use another third-generation cephalosporin at comparable dosage —

a Doses are for adults with normal renal function. Doses of gentamicin, streptomycin, and vancomycin must be adjusted for reduced renal function. Ideal body weight is used to calculate doses of gentamicin and streptomycin per kilogram (men = 50 kg + 2.3 kg per inch over 5 feet; women = 45.5 kg + 2.3 kg per inch over 5 feet). b MIC, ≤0.1 g/mL. c Desirable peak vancomycin level 1 h after completion of a 1-h infusion is 30–45 µg/mL. d Aminoglycosides should not be administered as single daily doses for enterococcal endocarditis and should be introduced as part of the initial treatment. Target peak and trough serum concentrations of divided-dose gentamicin 1 h after a 20- to 30-min infusion or IM injection are ∼3.5 µg/mL and ≤1 µg/mL, respectively; target peak and trough serum concentrations of streptomycin (timing as with gentamicin) are 20–35 µg/mL and 0.1 µg/mL and 0.5 µg/mL and 10-mm diameter) hypermobile vegetations with increased risk of embolism Persistent unexplained fever (≥10 days) in culturenegative native valve endocarditis Poorly responsive or relapsed endocarditis due to highly antibiotic-resistant enterococci or gram-negative bacilli a

Surgery must be carefully considered; findings are often combined with other indications to prompt surgery.

worsening valve dysfunction is the major indication for cardiac surgical treatment of endocarditis. Of patients with moderate to severe heart failure due to valve dysfunction who are treated medically, 60–90% die within 6 months. In this setting, surgical treatment improves outcome, with mortality rates of 20% in native valve endocarditis and 35–55% in prosthetic valve infection. Surgery can relieve functional stenosis due to large vegetations or restore competence to damaged regurgitant valves. infection This complication, which occurs in 10–15% of native valve and 45–60% of prosthetic valve infections, is suggested by persistent unexplained fever during appropriate therapy, new electrocardiographic conduction disturbances, and pericarditis. Extension can occur from any valve but is most common with aortic valve infection. TEE with color Doppler is the test of choice to detect perivalvular abscesses (sensitivity, ≥85%). Although occasional perivalvular infections are cured medically, surgery is warranted when fever persists, fistulae develop, prostheses are dehisced and unstable, and invasive infection relapses after appropriate treatment. Cardiac rhythm

Perivalvular

TABLE 25-6

287

TIMING OF CARDIAC SURGICAL INTERVENTION IN PATIENTS WITH ENDOCARDITIS INDICATION FOR SURGICAL INTERVENTION CONFLICTING EVIDENCE, BUT MAJORITY OF OPINIONS FAVOR SURGERY

TIMING

STRONG SUPPORTING EVIDENCE

Emergent (same day)

Acute aortic regurgitation plus preclosure of mitral valve Sinus of Valsalva abscess ruptured into right heart Rupture into pericardial sac Valve obstruction by vegetation Unstable (dehisced) prosthesis Acute aortic or mitral regurgitation with heart failure (New York Heart Association class III or IV) Septal perforation Perivalvular extension of infection with/without new electrocardiographic conduction system changes Lack of effective antibiotic therapy Progressive paravalvular prosthetic regurgitation Valve dysfunction plus persisting infection after ≥7–10 days of antimicrobial therapy Fungal (mold) endocarditis

Urgent (within 1–2 days)

Elective (earlier usually preferred)

Major embolus plus persisting large vegetation (>10 mm in diameter)

Staphylococcal PVE Early PVE (≤2 months after valve surgery) Fungal endocarditis (Candida spp.) Antibiotic-resistant organisms

infection Continued positive blood cultures or otherwise-unexplained persistent fevers (in patients with either blood culture–positive or –negative endocarditis) despite optimal antibiotic therapy may reflect uncontrolled infection and may warrant surgery. Surgical treatment is also advised for endocarditis caused by organisms against which clinical experience indicates that effective antimicrobial therapy is lacking. This category includes infections caused by yeasts, fungi, P. aeruginosa, other highly resistant gramnegative bacilli, Brucella species, and probably C. burnetii.

Uncontrolled

S. aureus endocarditis Mortality rates for S. aureus prosthetic valve endocarditis exceed 70% with medical treatment but are reduced to 25% with surgical treatment. In patients with intracardiac complications associated with S. aureus prosthetic valve infection, surgical treatment reduces the mortality rate twentyfold. Surgical treatment should be considered for patients with S. aureus native aortic or mitral valve infection who have TTE-demonstrable vegetations and remain septic during the initial week of therapy. Isolated tricuspid valve endocarditis, even with persistent fever, rarely requires surgery.

Prevention of systemic emboli Death and

persisting morbidity due to emboli are largely limited to patients suffering occlusion of cerebral or coronary arteries. Echocardiographic determination of vegetation size and anatomy, although predictive of patients at high risk of systemic emboli, does not identify those patients in whom the benefits of surgery to prevent emboli clearly exceed the risks of the surgical procedure and an implanted prosthetic valve. Net benefits favoring surgery are most likely when the risk of embolism is high and other surgical benefits can be achieved simultaneously—e.g., repair of a moderately dysfunctional valve or debridement of a paravalvular abscess. Reduced overall risks of surgical intervention (e.g., use of vegetation resection and valve repair to avoid insertion of a prosthesis) make the benefit-to-risk ratio more favorable and this intervention more attractive. Timing of Cardiac Surgery In general, when

indications for surgical treatment of infective endocarditis are identified, surgery should not be delayed simply to permit additional antibiotic therapy, since this course of action increases the risk of death (Table 25-6). Delay is justified only when infection is controlled and congestive heart failure is fully compensated with medical therapy. After 14 days of recommended antibiotic therapy,

Infective Endocarditis

must be monitored since high-grade heart block may require insertion of a pacemaker.

CHAPTER 25

Note: PVE, prosthetic valve endocarditis. Source: Adapted from L Olaison, G Pettersson: Infect Dis Clin North Am 16:453, 2002.

288

excised valves are culture-negative in 99% and 50% of patients with streptococcal and S. aureus endocarditis, respectively. Recrudescent endocarditis involving a new implanted prosthetic valve follows surgery in 2% of patients with culture-positive native valve endocarditis and in 6–15% of patients with active prosthetic valve endocarditis. These risks are more acceptable than the high mortality rates that result when surgery is inappropriately delayed or not performed. Among patients who have experienced a neurologic complication of endocarditis, further neurologic deterioration can occur as a consequence of cardiac surgery. The risk of significant neurologic exacerbation is related to the interval between the complication and the surgery. Whenever feasible, cardiac surgery should be delayed for 2–3 weeks after a nonhemorrhagic embolic stroke and for 4 weeks after a hemorrhagic embolic stroke. A ruptured mycotic aneurysm should be clipped and cerebral edema allowed to resolve before cardiac surgery. Antibiotic Therapy after Cardiac Surgery

SECTION IV Disorders of the Heart

Bacteria visible in Gram-stained preparations of excised valves do not necessarily indicate a failure of antibiotic therapy. Organisms have been detected on Gram’s stain—or their DNA has been detected by PCR—in excised valves from 45% of patients who have successfully completed the recommended therapy for endocarditis. In only 7% of these patients are the organisms, most of which are unusual and antibiotic resistant, cultured from the valve. Despite the detection of organisms or their DNA, relapse of endocarditis after surgery is uncommon. Thus, for uncomplicated native valve infection caused by susceptible organisms in conjunction with negative valve cultures, the duration of preoperative plus postoperative treatment should equal the total duration of recommended therapy, with ∼2 weeks of treatment administered after surgery. For endocarditis complicated by paravalvular abscess, partially treated prosthetic valve infection, or cases with culture-positive valves, a full course of therapy should be given postoperatively. Complications Splenic abscess develops in 3–5% of patients with endocarditis. Effective therapy requires either image-guided percutaneous drainage or splenectomy. Mycotic aneurysms occur in 2–15% of endocarditis patients; half of these cases involve the cerebral arteries and present as headaches, focal neurologic symptoms, or hemorrhage. Cerebral aneurysms should be monitored by angiography. Some will resolve with effective antimicrobial therapy, but those that persist, enlarge, or leak should be treated surgically if possible. Extracerebral aneurysms present as local pain, a mass, local ischemia, or bleeding; these aneurysms are treated by resection.

Extracardiac

OUTCOME Older age, severe comorbid conditions, delayed diagnosis, involvement of prosthetic valves or the aortic valve, an invasive (S. aureus) or antibiotic-resistant (P. aeruginosa, yeast) pathogen, intracardiac complications, and major neurologic complications adversely impact outcome. Death and poor outcome often are related not to failure of antibiotic therapy but rather to the interactions of comorbidities and endocarditis-related end-organ complications. Overall survival rates for patients with native valve endocarditis caused by viridans streptococci, HACEK organisms, or enterococci (susceptible to synergistic therapy) are 85–90%. For S. aureus native valve endocarditis in patients who do not inject drugs, survival rates are 55–70%, whereas 85–90% of injection drug users survive this infection. Prosthetic valve endocarditis beginning within 2 months of valve replacement results in mortality rates of 40–50%, whereas rates are only 10–20% in later-onset cases.

PREVENTION Antibiotic prophylaxis has been recommended by the American Heart Association in conjunction with selected procedures considered to entail a risk for bacteremia and endocarditis. The benefits of prophylaxis, however, are not established and in fact may be modest: only 50% of patients presenting with native valve endocarditis know that they have a predisposing valve lesion, most endocarditis cases do not follow a procedure, and 35% of cases are caused by organisms not targeted by prophylaxis. Dental treatments, the procedures most widely accepted as predisposing to endocarditis, are no more frequent during the 3 months preceding endocarditis than in uninfected matched controls. Furthermore, the frequency and magnitude of bacteremia associated with dental procedures and routine daily activities (e.g., tooth brushing and flossing) are similar. Because patients undergo dental procedures infrequently, exposure of endocarditisvulnerable cardiac structures to bacteremia-causing oral cavity organisms is notably greater from routine daily activities than from dental care. It is estimated that annual exposure of heart valves to bacteremia-causing organisms may be 5.6 million times greater from routine daily activity than from a tooth extraction. The relation of gastrointestinal and genitourinary procedures to subsequent endocarditis is more tenuous than that of dental procedures. Antibiotic prophylaxis, if 100% effective, likely prevents only a small number of cases of endocarditis; nevertheless, it is possible that rare cases are prevented. Weighing the potential benefits, potential adverse events, and costs associated with antibiotic prophylaxis, the expert committee of the American Heart Association has dramatically restricted the recommendations for antibiotic prophylaxis.

TABLE 25-7 ANTIBIOTIC REGIMENS FOR PROPHYLAXIS OF ENDOCARDITIS IN ADULTS WITH HIGH-RISK CARDIAC LESIONS a,b A. Standard oral regimen 1. Amoxicillin 2.0 g PO 1 h before procedure B. Inability to take oral medication 1. Ampicillin 2.0 g IV or IM within 1 h before procedure C. Penicillin allergy 1. Clarithromycin or azithromycin 500 mg PO 1 h before procedure 2. Cephalexinc 2.0 g PO 1 h before procedure 3. Clindamycin 600 mg PO 1 h before procedure D. Penicillin allergy, inability to take oral medication 1. Cefazolinc or ceftriaxonec 1.0 g IV or IM 30 min before procedure 2. Clindamycin 600 mg IV or IM 1 h before procedure a

Dosing for children: for amoxicillin, ampicillin, cephalexin, or cefadroxil, use 50 mg/kg PO; cefazolin, 25 mg/kg IV; clindamycin, 20 mg/kg PO, 25 mg/kg IV; clarithromycin, 15 mg/kg PO; and vancomycin, 20 mg/kg IV. b For high-risk lesions, see Table 25-8. Prophylaxis is not advised for other lesions. c Do not use cephalosporins in patients with immediate hypersensitivity (urticaria, angioedema, anaphylaxis) to penicillin. Source: W Wilson et al: Circulation, published online 4/19/07.

HIGH-RISK CARDIAC LESIONS FOR WHICH ENDOCARDITIS PROPHYLAXIS IS ADVISED BEFORE DENTAL PROCEDURES Prosthetic heart valves Prior endocarditis Unrepaired cyanotic congenital heart disease, including palliative shunts or conduits Completely repaired congenital heart defects during the 6 months after repair Incompletely repaired congenital heart disease with residual defects adjacent to prosthetic material Valvulopathy developing after cardiac transplantation Source: W Wilson et al: Circulation, published online 4/19/07.

BADDOUR LM et al: Diagnosis, antimicrobial therapy, and management of complications. A statement for healthcare professionals from the Committee on Rheumatic Fever, Endocarditis, and Kawasaki Disease, Council on Cardiovascular Disease in the Young, and the Councils on Clinical Cardiology, Stroke, and Cardiovascular Surgery and Anesthesia, American Heart Association. Circulation 111:e394, 2005 DURACK DT (ed): Infective endocarditis. Infect Dis Clin North Am 16:255, 2002 FOWLER VG JR et al: Endocarditis and intravascular infections, in Principles and Practice of Infectious Diseases, 6th ed, GL Mandell et al (eds). Philadelphia, Elsevier Churchill Livingstone, 2005, pp 975–1021 HORSTKOTTE D et al: Guidelines on prevention, diagnosis and treatment of infective endocarditis. Executive summary, The Task Force on Infective Endocarditis of the European Society of Cardiology. Eur Heart J 25:267, 2004 K ARCHMER AW: Infective endocarditis, in Heart Disease, 8th ed, E Braunwald et al (eds). Philadelphia, Elsevier Saunders, 2008 ———, LONGWORTH DL: Infections of intracardiac devices. Cardiol Clin 21:253, 2003 LI JS et al: Proposed modifications to the Duke criteria for the diagnosis of infective endocarditis. Clin Infect Dis 30:633, 2000 MOREILLON P, Que YA: Infective endocarditis. Lancet 363:139, 2004 M ORRIS AJ et al: Bacteriological outcome after valve surgery for active infective endocarditis: Implications for duration of treatment after surgery (abstract). Clin Infect Dis 41:187, 2005 VIKRAM HR et al: Impact of valve surgery on 6-month mortality in adults with complicated, left-sided native valve endocarditis: A propensity analysis. JAMA 290:3207, 2003 WILSON W et al: Prevention of infective endocarditis. Guidelines from the American Heart Association. A guideline from the American Heart Association Rheumatic Fever, Endocarditis, and Kawasaki Disease Committee, Council on Cardiovascular Disease in the Young, and the Council on Clinical Cardiology, Council on Cardiovascular Surgery and Anesthesia, and the Quality of Care and Outcomes Research Interdisciplinary Working Group. Circulation 116:1736, 2007

Infective Endocarditis

TABLE 25-8

FURTHER READINGS

CHAPTER 25

Prophylactic antibiotics (Table 25-7) are advised only for those patients at highest risk for severe morbidity or death from endocarditis (Table 25-8). Prophylaxis is recommended only for dental procedures wherein there is manipulation of gingival tissue or the periapical region of

the teeth or perforation of the oral mucosa (including 289 surgery on the respiratory tract). Although prophylaxis is not advised for patients undergoing gastrointestinal or genitourinary tract procedures, it is recommended that effective treatment be given to these high-risk patients before or when they undergo procedures on an infected genitourinary tract or on infected skin and related soft tissue. Maintaining good dental hygiene is also advised. (W Wilson et al.)

CHAPTER 26

ACUTE RHEUMATIC FEVER Jonathan R. Carapetis

Epidemiology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Pathogenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290 Clinical Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292 Prognosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 Prevention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295 ■ Further Readings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296

Acute rheumatic fever (ARF) is a multisystem disease resulting from an autoimmune reaction to infection with group A streptococci. Although many parts of the body may be affected, almost all of the manifestations resolve completely. The exception is cardiac valvular damage [rheumatic heart disease (RHD)], which may persist after the other features have disappeared.

Although ARF and RHD are relatively common in all developing countries, they occur at particularly elevated rates in certain regions. The “hot spots” are sub-Saharan Africa, Pacific nations, Australasia, and the Indian subcontinent (Fig. 26-1).

ARF and RHD are diseases of poverty.They were common in all countries until the early twentieth century, when their incidence began to decline in industrialized nations.This decline was largely attributable to improved living conditions—particularly less crowded housing and better hygiene—which resulted in reduced transmission of group A streptococci.The introduction of antibiotics and improved systems of medical care had a supplemental effect. Recurrent outbreaks of ARF began in the 1980s in the Rocky Mountain states of the United States, where elevated rates persist. The virtual disappearance of ARF and reduction in the incidence of RHD in industrialized countries during the twentieth century unfortunately was not replicated in developing countries, where these diseases continue unabated. RHD is the most common cause of heart disease in children in developing countries and is a major cause of mortality and morbidity in adults as well. It was recently estimated that between 15 and 19 million people worldwide are affected by RHD, with approximately one-quarter of a million deaths occurring each year. Some 95% of ARF cases and RHD deaths now occur in developing countries.

ARF is mainly a disease of children aged 5–14 years. Initial episodes become less common in older adolescents and young adults and are rare in persons older than 30 years. By contrast, recurrent episodes of ARF remain relatively common in adolescents and young adults. This pattern contrasts with the prevalence of RHD, which peaks between 25 and 40 years.There is no clear gender association for ARF, but RHD more commonly affects females, sometimes up to twice as frequently as males.

EPIDEMIOLOGY

PATHOGENESIS Organism Factors Based on currently available evidence, ARF is exclusively caused by infection of the upper respiratory tract with group A streptococci. It is now thought that any strain of group A streptococcus has the potential to cause ARF. Potential role of skin infection and of groups C and G streptococci are currently being investigated. It has been postulated that a series of preceding streptococcal infections is needed to “prime” the immune system prior to the final infection that directly causes disease.

290

291

FIGURE 26-1 Prevalence of rheumatic heart disease in children aged 5–14 years. Circles within Australia and New Zealand represent indigenous populations, and also Pacific Islanders in New Zealand. (Reprinted with permission from JR Carapetis et al: Lancet Infect Dis.)

Prevalence of rheumatic heart disease (cases per 1000) 0–3

1– 0

1– 3

3–5

0–8

1– 8

2– 2

5–7

Approximately 3–6% of any population may be susceptible to ARF, and this proportion does not vary dramatically between populations. Findings of familial clustering of cases and concordance in monozygotic twins— particularly for chorea—confirm that susceptibility to ARF is an inherited characteristic. Particular HLA class II alleles appear to be strongly associated with susceptibility. Associations have also been described with high levels of circulating mannose-binding lectin and polymorphisms of transforming growth factor β1 gene and immunoglobulin genes. High-level expression of a particular alloantigen present on B cells, D8-17, has been found in patients with a history of ARF in many populations, with intermediatelevel expression in first-degree family members, suggesting that this may be a marker of inherited susceptibility.

When a susceptible host encounters a group A streptococcus, an autoimmune reaction results which leads to damage to the human tissues as a result of cross-reactivity between epitopes on the organism and the host (Fig. 26-2). Epitopes present in the cell wall, cell membrane, and the A, B, and C repeat regions of the streptococcal M protein are immunologically similar to molecules in human myosin, tropomyosin, keratin, actin, laminin, vimentin, and N-acetylglucosamine. This molecular mimicry is the basis for the autoimmune response that leads to ARF. It has been hypothesized that human molecules—particularly epitopes in cardiac myosin—result in T cell sensitization. These T cells are then recalled following subsequent exposure to group A streptococci bearing immunologically similar epitopes.

Environmental factors, especially overcrowding

Precipitating event: infection with a strain of group A streptococcus carrying specific virulence factors Repeated or ongoing infections possibly driving the valvular inflammatory response

Repeated group A streptococcus infections Susceptible host

Priming of immune response

First episode of ARF

RHD

Episodes of recurrent ARF Molecular mimicry between group A streptococcus antigens and host tissues

Exaggerated T-cell mediated immune response

Genetically determined host factors

FIGURE 26-2 Pathogenetic pathway for acute rheumatic fever and rheumatic heart disease. (Reprinted with permission from Lancet 366:155, 2005.)

Acute Rheumatic Fever

The Immune Response

CHAPTER 26

Host Factors

292

However, myosin cross-reactivity with M protein does not explain the valvular damage that is the hallmark of rheumatic carditis, given that myosin is not present in valvular tissue. The link may be laminin, another α-helical coiled-coil protein like myosin and M protein, which is found in cardiac endothelium and is recognized by anti-myosin, anti-M protein T cells. Moreover, antibodies to cardiac valve tissue cross-react with the N-acetylglucosamine of group A streptococcal carbohydrate, and there is some evidence that these antibodies may be responsible for valvular damage.

CLINICAL FEATURES

SECTION IV

There is a latent period of ∼3 weeks (1–5 weeks) between the precipitating group A streptococcal infection and the appearance of the clinical features of ARF. The exceptions are chorea and indolent carditis, which may follow prolonged latent periods lasting up to 6 months.Although many patients report a prior sore throat, the preceding group A streptococcal infection is commonly subclinical; in these cases it can only be confirmed using streptococcal antibody testing. The most common clinical presentation of ARF is polyarthritis and fever. Polyarthritis is present in 60–75% of cases and carditis in 50–60%. The prevalence of chorea in ARF varies substantially between populations, ranging from